diff --git a/tests/Aggregation/AbstractSimpleAggregationTest.php b/tests/Aggregation/AbstractSimpleAggregationTest.php
index 2580fb5822..2e2740917a 100644
--- a/tests/Aggregation/AbstractSimpleAggregationTest.php
+++ b/tests/Aggregation/AbstractSimpleAggregationTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\AbstractSimpleAggregation;
diff --git a/tests/Aggregation/AdjacencyMatrixTest.php b/tests/Aggregation/AdjacencyMatrixTest.php
index ac02034b0e..af9f28960d 100644
--- a/tests/Aggregation/AdjacencyMatrixTest.php
+++ b/tests/Aggregation/AdjacencyMatrixTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\AdjacencyMatrix;
diff --git a/tests/Aggregation/AggregationMetadataTest.php b/tests/Aggregation/AggregationMetadataTest.php
index 0372a6d0f8..771c1a34ed 100644
--- a/tests/Aggregation/AggregationMetadataTest.php
+++ b/tests/Aggregation/AggregationMetadataTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\Cardinality;
diff --git a/tests/Aggregation/AutoDateHistogramTest.php b/tests/Aggregation/AutoDateHistogramTest.php
index 244714bebd..7e4927b048 100644
--- a/tests/Aggregation/AutoDateHistogramTest.php
+++ b/tests/Aggregation/AutoDateHistogramTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\AutoDateHistogram;
diff --git a/tests/Aggregation/AvgBucketTest.php b/tests/Aggregation/AvgBucketTest.php
index 5f8767b8b6..48f8d34f36 100644
--- a/tests/Aggregation/AvgBucketTest.php
+++ b/tests/Aggregation/AvgBucketTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\Avg;
diff --git a/tests/Aggregation/AvgTest.php b/tests/Aggregation/AvgTest.php
index aa234cbec0..73aae6fb43 100644
--- a/tests/Aggregation/AvgTest.php
+++ b/tests/Aggregation/AvgTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\Avg;
diff --git a/tests/Aggregation/BaseAggregationTest.php b/tests/Aggregation/BaseAggregationTest.php
index 60062e913b..3aa73d3a6f 100644
--- a/tests/Aggregation/BaseAggregationTest.php
+++ b/tests/Aggregation/BaseAggregationTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Test\Base;
diff --git a/tests/Aggregation/BucketScriptTest.php b/tests/Aggregation/BucketScriptTest.php
index 7c5ff05377..58dad1130d 100644
--- a/tests/Aggregation/BucketScriptTest.php
+++ b/tests/Aggregation/BucketScriptTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\BucketScript;
diff --git a/tests/Aggregation/BucketSelectorTest.php b/tests/Aggregation/BucketSelectorTest.php
index cb31a88036..50d8224020 100644
--- a/tests/Aggregation/BucketSelectorTest.php
+++ b/tests/Aggregation/BucketSelectorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\BucketSelector;
diff --git a/tests/Aggregation/CardinalityTest.php b/tests/Aggregation/CardinalityTest.php
index 8c18cca1d7..997467be42 100644
--- a/tests/Aggregation/CardinalityTest.php
+++ b/tests/Aggregation/CardinalityTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\Cardinality;
diff --git a/tests/Aggregation/ChildrenTest.php b/tests/Aggregation/ChildrenTest.php
index 0d3e6876a8..4687e0db7b 100644
--- a/tests/Aggregation/ChildrenTest.php
+++ b/tests/Aggregation/ChildrenTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\Children;
diff --git a/tests/Aggregation/CompositeTest.php b/tests/Aggregation/CompositeTest.php
index f1e87163ed..de750576d9 100644
--- a/tests/Aggregation/CompositeTest.php
+++ b/tests/Aggregation/CompositeTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\Composite;
diff --git a/tests/Aggregation/CumulativeSumTest.php b/tests/Aggregation/CumulativeSumTest.php
index d985823e5f..61892cb09b 100644
--- a/tests/Aggregation/CumulativeSumTest.php
+++ b/tests/Aggregation/CumulativeSumTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\CumulativeSum;
diff --git a/tests/Aggregation/DateHistogramTest.php b/tests/Aggregation/DateHistogramTest.php
index d164be9a45..af93c6d238 100644
--- a/tests/Aggregation/DateHistogramTest.php
+++ b/tests/Aggregation/DateHistogramTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\DateHistogram;
diff --git a/tests/Aggregation/DateRangeTest.php b/tests/Aggregation/DateRangeTest.php
index 846405061c..9e0dea6616 100644
--- a/tests/Aggregation/DateRangeTest.php
+++ b/tests/Aggregation/DateRangeTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastic\Elasticsearch\Exception\ClientResponseException;
diff --git a/tests/Aggregation/DerivativeTest.php b/tests/Aggregation/DerivativeTest.php
index 8be63a119f..a0859a7292 100644
--- a/tests/Aggregation/DerivativeTest.php
+++ b/tests/Aggregation/DerivativeTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\DateHistogram;
diff --git a/tests/Aggregation/DiversifiedSamplerTest.php b/tests/Aggregation/DiversifiedSamplerTest.php
index 477bbe755b..8dd4cf7938 100755
--- a/tests/Aggregation/DiversifiedSamplerTest.php
+++ b/tests/Aggregation/DiversifiedSamplerTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\DiversifiedSampler;
diff --git a/tests/Aggregation/ExtendedStatsBucketTest.php b/tests/Aggregation/ExtendedStatsBucketTest.php
index f7d5404f0a..5f726b7b11 100644
--- a/tests/Aggregation/ExtendedStatsBucketTest.php
+++ b/tests/Aggregation/ExtendedStatsBucketTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\ExtendedStatsBucket;
diff --git a/tests/Aggregation/ExtendedStatsTest.php b/tests/Aggregation/ExtendedStatsTest.php
index b10b56b18f..a189d93e52 100644
--- a/tests/Aggregation/ExtendedStatsTest.php
+++ b/tests/Aggregation/ExtendedStatsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\ExtendedStats;
diff --git a/tests/Aggregation/FilterTest.php b/tests/Aggregation/FilterTest.php
index 3aec7e4068..2a692845e4 100644
--- a/tests/Aggregation/FilterTest.php
+++ b/tests/Aggregation/FilterTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\Avg;
diff --git a/tests/Aggregation/FiltersTest.php b/tests/Aggregation/FiltersTest.php
index 65aab2375c..c102194e88 100644
--- a/tests/Aggregation/FiltersTest.php
+++ b/tests/Aggregation/FiltersTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\Avg;
diff --git a/tests/Aggregation/GeoBoundsTest.php b/tests/Aggregation/GeoBoundsTest.php
index 63e0867b7d..e67fabd838 100644
--- a/tests/Aggregation/GeoBoundsTest.php
+++ b/tests/Aggregation/GeoBoundsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\GeoBounds;
diff --git a/tests/Aggregation/GeoCentroidTest.php b/tests/Aggregation/GeoCentroidTest.php
index a79301030c..075e925f3f 100644
--- a/tests/Aggregation/GeoCentroidTest.php
+++ b/tests/Aggregation/GeoCentroidTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\GeoCentroid;
diff --git a/tests/Aggregation/GeoDistanceTest.php b/tests/Aggregation/GeoDistanceTest.php
index 4fa3f08251..d4246cc067 100644
--- a/tests/Aggregation/GeoDistanceTest.php
+++ b/tests/Aggregation/GeoDistanceTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\GeoDistance;
diff --git a/tests/Aggregation/GeohashGridTest.php b/tests/Aggregation/GeohashGridTest.php
index 551aa211c0..0d516a5c39 100644
--- a/tests/Aggregation/GeohashGridTest.php
+++ b/tests/Aggregation/GeohashGridTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\GeohashGrid;
diff --git a/tests/Aggregation/GeotileGridAggregationTest.php b/tests/Aggregation/GeotileGridAggregationTest.php
index 8d6069cf43..58927b95e3 100644
--- a/tests/Aggregation/GeotileGridAggregationTest.php
+++ b/tests/Aggregation/GeotileGridAggregationTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\GeotileGridAggregation;
diff --git a/tests/Aggregation/GlobalAggregationTest.php b/tests/Aggregation/GlobalAggregationTest.php
index 595724ce9c..8e2c08ccf2 100644
--- a/tests/Aggregation/GlobalAggregationTest.php
+++ b/tests/Aggregation/GlobalAggregationTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\Avg;
diff --git a/tests/Aggregation/HistogramTest.php b/tests/Aggregation/HistogramTest.php
index 1aa9411421..3fb4d7f4ab 100644
--- a/tests/Aggregation/HistogramTest.php
+++ b/tests/Aggregation/HistogramTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\Histogram;
diff --git a/tests/Aggregation/IpRangeTest.php b/tests/Aggregation/IpRangeTest.php
index 337f344712..2d989267b2 100644
--- a/tests/Aggregation/IpRangeTest.php
+++ b/tests/Aggregation/IpRangeTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\IpRange;
diff --git a/tests/Aggregation/MaxTest.php b/tests/Aggregation/MaxTest.php
index c7e0a9477c..b2482800f3 100644
--- a/tests/Aggregation/MaxTest.php
+++ b/tests/Aggregation/MaxTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\Max;
diff --git a/tests/Aggregation/MinTest.php b/tests/Aggregation/MinTest.php
index 1367cce6b7..dfcca34c80 100644
--- a/tests/Aggregation/MinTest.php
+++ b/tests/Aggregation/MinTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\Min;
diff --git a/tests/Aggregation/MissingTest.php b/tests/Aggregation/MissingTest.php
index 06f72a4f80..53ecfb061a 100644
--- a/tests/Aggregation/MissingTest.php
+++ b/tests/Aggregation/MissingTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\Missing;
diff --git a/tests/Aggregation/NestedTest.php b/tests/Aggregation/NestedTest.php
index f50345c769..a134d992cb 100644
--- a/tests/Aggregation/NestedTest.php
+++ b/tests/Aggregation/NestedTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\Min;
diff --git a/tests/Aggregation/NormalizeAggregationTest.php b/tests/Aggregation/NormalizeAggregationTest.php
index cc830453bb..3f873a20ef 100644
--- a/tests/Aggregation/NormalizeAggregationTest.php
+++ b/tests/Aggregation/NormalizeAggregationTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\DateHistogram;
diff --git a/tests/Aggregation/ParentAggregationTest.php b/tests/Aggregation/ParentAggregationTest.php
index dd63b953e8..aff7383767 100644
--- a/tests/Aggregation/ParentAggregationTest.php
+++ b/tests/Aggregation/ParentAggregationTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\ParentAggregation;
diff --git a/tests/Aggregation/PercentilesBucketTest.php b/tests/Aggregation/PercentilesBucketTest.php
index c8a934c29e..73b249e83f 100644
--- a/tests/Aggregation/PercentilesBucketTest.php
+++ b/tests/Aggregation/PercentilesBucketTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\Avg;
diff --git a/tests/Aggregation/PercentilesTest.php b/tests/Aggregation/PercentilesTest.php
index 5fd7c0f242..6733b2a5e6 100644
--- a/tests/Aggregation/PercentilesTest.php
+++ b/tests/Aggregation/PercentilesTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\Percentiles;
diff --git a/tests/Aggregation/RangeTest.php b/tests/Aggregation/RangeTest.php
index d9485d2458..7c49223b75 100644
--- a/tests/Aggregation/RangeTest.php
+++ b/tests/Aggregation/RangeTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\Range;
diff --git a/tests/Aggregation/ReverseNestedTest.php b/tests/Aggregation/ReverseNestedTest.php
index 66bf18d307..1f5984835a 100644
--- a/tests/Aggregation/ReverseNestedTest.php
+++ b/tests/Aggregation/ReverseNestedTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\Nested;
diff --git a/tests/Aggregation/SamplerTest.php b/tests/Aggregation/SamplerTest.php
index f3ecf67337..6e2e0d160e 100644
--- a/tests/Aggregation/SamplerTest.php
+++ b/tests/Aggregation/SamplerTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\Sampler;
diff --git a/tests/Aggregation/ScriptTest.php b/tests/Aggregation/ScriptTest.php
index 0b0ad23ba8..94d2bde6eb 100644
--- a/tests/Aggregation/ScriptTest.php
+++ b/tests/Aggregation/ScriptTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\Sum;
diff --git a/tests/Aggregation/ScriptedMetricTest.php b/tests/Aggregation/ScriptedMetricTest.php
index 42d2c451fa..31b579f99d 100644
--- a/tests/Aggregation/ScriptedMetricTest.php
+++ b/tests/Aggregation/ScriptedMetricTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\ScriptedMetric;
diff --git a/tests/Aggregation/SerialDiffTest.php b/tests/Aggregation/SerialDiffTest.php
index 5439147519..89923172de 100644
--- a/tests/Aggregation/SerialDiffTest.php
+++ b/tests/Aggregation/SerialDiffTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\DateHistogram;
diff --git a/tests/Aggregation/SignificantTermsTest.php b/tests/Aggregation/SignificantTermsTest.php
index fd08f29fe7..ad210eff5f 100644
--- a/tests/Aggregation/SignificantTermsTest.php
+++ b/tests/Aggregation/SignificantTermsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\SignificantTerms;
diff --git a/tests/Aggregation/StatsBucketTest.php b/tests/Aggregation/StatsBucketTest.php
index 0e692f3fbd..be72d1f54d 100644
--- a/tests/Aggregation/StatsBucketTest.php
+++ b/tests/Aggregation/StatsBucketTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\GapPolicyInterface;
diff --git a/tests/Aggregation/StatsTest.php b/tests/Aggregation/StatsTest.php
index a65db25736..352576625c 100644
--- a/tests/Aggregation/StatsTest.php
+++ b/tests/Aggregation/StatsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\Stats;
diff --git a/tests/Aggregation/SumBucketTest.php b/tests/Aggregation/SumBucketTest.php
index 9833d64de7..b622da6160 100644
--- a/tests/Aggregation/SumBucketTest.php
+++ b/tests/Aggregation/SumBucketTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\GapPolicyInterface;
diff --git a/tests/Aggregation/SumTest.php b/tests/Aggregation/SumTest.php
index bad6588a14..5fef5daaa4 100644
--- a/tests/Aggregation/SumTest.php
+++ b/tests/Aggregation/SumTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\Sum;
diff --git a/tests/Aggregation/TermsTest.php b/tests/Aggregation/TermsTest.php
index 41659f7b92..befeb274db 100644
--- a/tests/Aggregation/TermsTest.php
+++ b/tests/Aggregation/TermsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\Composite;
diff --git a/tests/Aggregation/TopHitsTest.php b/tests/Aggregation/TopHitsTest.php
index 43eddab24a..0cfe0e3126 100644
--- a/tests/Aggregation/TopHitsTest.php
+++ b/tests/Aggregation/TopHitsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\AbstractAggregation;
diff --git a/tests/Aggregation/ValueCountTest.php b/tests/Aggregation/ValueCountTest.php
index 4f122ac269..7ec62c91cf 100644
--- a/tests/Aggregation/ValueCountTest.php
+++ b/tests/Aggregation/ValueCountTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\ValueCount;
diff --git a/tests/Aggregation/WeightedAvgTest.php b/tests/Aggregation/WeightedAvgTest.php
index be344b4af7..090026486d 100644
--- a/tests/Aggregation/WeightedAvgTest.php
+++ b/tests/Aggregation/WeightedAvgTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Aggregation;
 
 use Elastica\Aggregation\WeightedAvg;
diff --git a/tests/Base.php b/tests/Base.php
index e77ab3dd5e..2fceea4fa8 100644
--- a/tests/Base.php
+++ b/tests/Base.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test;
 
 use Elastic\Transport\NodePool\Resurrect\NoResurrect;
@@ -52,7 +54,7 @@ protected function _getClient(array $config = [], ?LoggerInterface $logger = nul
     {
         $config['hosts'] ??= [$this->_getHost().':'.$this->_getPort()];
 
-        $config['transport_config']['node_pool'] = $config['transport_config']['node_pool'] ?? new TraceableSimpleNodePool(
+        $config['transport_config']['node_pool'] ??= new TraceableSimpleNodePool(
             new RoundRobin(),
             new NoResurrect()
         );
diff --git a/tests/BasePipeline.php b/tests/BasePipeline.php
index 6d0b10c2dc..5737fd4e20 100644
--- a/tests/BasePipeline.php
+++ b/tests/BasePipeline.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test;
 
 use Elastica\Pipeline;
diff --git a/tests/Bulk/Action/AbstractDocumentTest.php b/tests/Bulk/Action/AbstractDocumentTest.php
index d468f8ff0e..2f68771cda 100644
--- a/tests/Bulk/Action/AbstractDocumentTest.php
+++ b/tests/Bulk/Action/AbstractDocumentTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Bulk\Action;
 
 use Elastica\Bulk\Action\AbstractDocument;
diff --git a/tests/Bulk/Action/UpdateDocumentTest.php b/tests/Bulk/Action/UpdateDocumentTest.php
index 93c619be99..7565d819e9 100644
--- a/tests/Bulk/Action/UpdateDocumentTest.php
+++ b/tests/Bulk/Action/UpdateDocumentTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Bulk\Action;
 
 use Elastica\Bulk\Action\UpdateDocument;
@@ -67,9 +69,9 @@ public function testUpdateDocumentAsUpsert(): void
         $this->assertTrue($action->hasSource());
 
         $expected = <<<'JSON'
-{"update":{"_id":"1","_index":"index"}}
-{"doc":{"foo":"bar"},"doc_as_upsert":true}
-JSON;
+            {"update":{"_id":"1","_index":"index"}}
+            {"doc":{"foo":"bar"},"doc_as_upsert":true}
+            JSON;
 
         $this->assertSame($expected, \trim((string) $action));
 
@@ -81,9 +83,9 @@ public function testUpdateDocumentAsUpsert(): void
         $action->setDocument($document);
 
         $expected = <<<'JSON'
-{"update":{"_id":"1","_index":"index"}}
-{"doc":{"foo":"bar"}}
-JSON;
+            {"update":{"_id":"1","_index":"index"}}
+            {"doc":{"foo":"bar"}}
+            JSON;
 
         $this->assertSame($expected, \trim((string) $action));
 
diff --git a/tests/Bulk/ActionTest.php b/tests/Bulk/ActionTest.php
index 644bf6440e..c4200f856a 100644
--- a/tests/Bulk/ActionTest.php
+++ b/tests/Bulk/ActionTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Bulk;
 
 use Elastica\Bulk\Action;
diff --git a/tests/Bulk/ResponseSetTest.php b/tests/Bulk/ResponseSetTest.php
index 56fba86240..ebf7ba8a22 100644
--- a/tests/Bulk/ResponseSetTest.php
+++ b/tests/Bulk/ResponseSetTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Bulk;
 
 use Elastica\Bulk;
diff --git a/tests/BulkTest.php b/tests/BulkTest.php
index c8fd59c333..982a1e0644 100644
--- a/tests/BulkTest.php
+++ b/tests/BulkTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test;
 
 use Elastica\Bulk;
@@ -385,13 +387,13 @@ public function testRawDocumentDataRequest(): void
         ;
 
         $expectedJson = <<<'JSON'
-{"index":{}}
-{"name":"Mister Fantastic"}
-{"index":{}}
-{"name":"Invisible Woman"}
-{"index":{}}
-{"name":"The Human Torch"}
-JSON;
+            {"index":{}}
+            {"name":"Mister Fantastic"}
+            {"index":{}}
+            {"name":"Invisible Woman"}
+            {"index":{}}
+            {"name":"The Human Torch"}
+            JSON;
 
         $expectedJson = \str_replace(\PHP_EOL, "\n", $expectedJson);
         $this->assertSame($expectedJson, \trim((string) $bulk));
diff --git a/tests/ClientConfigurationTest.php b/tests/ClientConfigurationTest.php
index 5566843811..0e32eb5224 100644
--- a/tests/ClientConfigurationTest.php
+++ b/tests/ClientConfigurationTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test;
 
 use Elastica\ClientConfiguration;
diff --git a/tests/ClientFunctionalTest.php b/tests/ClientFunctionalTest.php
index 78bf18b752..e6815777ad 100644
--- a/tests/ClientFunctionalTest.php
+++ b/tests/ClientFunctionalTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test;
 
 use Elastic\Elasticsearch\Response\Elasticsearch;
@@ -926,7 +928,7 @@ protected function setHttpClientOptions(HttpClientInterface $client, array $conf
         if (empty($config) && empty($clientOptions)) {
             return $client;
         }
-        $class = \get_class($client);
+        $class = $client::class;
         $adapterClass = AdapterOptions::HTTP_ADAPTERS[$class];
 
         $adapter = new $adapterClass();
diff --git a/tests/ClientTest.php b/tests/ClientTest.php
index f7ac859294..83e832cc49 100644
--- a/tests/ClientTest.php
+++ b/tests/ClientTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test;
 
 use Elastica\Client;
diff --git a/tests/Cluster/Health/IndexTest.php b/tests/Cluster/Health/IndexTest.php
index be86e5363e..fc8fa42ad6 100644
--- a/tests/Cluster/Health/IndexTest.php
+++ b/tests/Cluster/Health/IndexTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Cluster\Health;
 
 use Elastica\Cluster\Health\Index;
diff --git a/tests/Cluster/Health/ShardTest.php b/tests/Cluster/Health/ShardTest.php
index 26fc5ac400..56fb04e925 100644
--- a/tests/Cluster/Health/ShardTest.php
+++ b/tests/Cluster/Health/ShardTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Cluster\Health;
 
 use Elastica\Cluster\Health\Shard;
diff --git a/tests/Cluster/HealthTest.php b/tests/Cluster/HealthTest.php
index bb74b0e9e1..2dc050afab 100644
--- a/tests/Cluster/HealthTest.php
+++ b/tests/Cluster/HealthTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Cluster;
 
 use Elastica\Cluster\Health;
diff --git a/tests/Cluster/SettingsTest.php b/tests/Cluster/SettingsTest.php
index a9c00f4b0b..f0ffb4ab9c 100644
--- a/tests/Cluster/SettingsTest.php
+++ b/tests/Cluster/SettingsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Cluster;
 
 use Elastic\Elasticsearch\Exception\ClientResponseException;
diff --git a/tests/ClusterTest.php b/tests/ClusterTest.php
index 88d6beabed..feaba72eea 100644
--- a/tests/ClusterTest.php
+++ b/tests/ClusterTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test;
 
 use Elastica\Cluster;
diff --git a/tests/Collapse/CollapseTest.php b/tests/Collapse/CollapseTest.php
index 084d3696f8..9213b967f9 100644
--- a/tests/Collapse/CollapseTest.php
+++ b/tests/Collapse/CollapseTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Collapse;
 
 use Elastica\Collapse;
diff --git a/tests/DeprecatedClassBase.php b/tests/DeprecatedClassBase.php
index 483d13a88d..042fda3a72 100644
--- a/tests/DeprecatedClassBase.php
+++ b/tests/DeprecatedClassBase.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test;
 
 /**
diff --git a/tests/DocumentTest.php b/tests/DocumentTest.php
index 324105f4da..cefc2a5c67 100644
--- a/tests/DocumentTest.php
+++ b/tests/DocumentTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test;
 
 use Elastica\Document;
diff --git a/tests/ExampleTest.php b/tests/ExampleTest.php
index bc9cd473e1..303dcfa550 100644
--- a/tests/ExampleTest.php
+++ b/tests/ExampleTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test;
 
 use Elastica\Document;
diff --git a/tests/Exception/AbstractExceptionTest.php b/tests/Exception/AbstractExceptionTest.php
index bba69c8782..361f3ab64a 100644
--- a/tests/Exception/AbstractExceptionTest.php
+++ b/tests/Exception/AbstractExceptionTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Exception;
 
 use Elastica\Exception\ExceptionInterface;
diff --git a/tests/Exception/Bulk/Response/ActionExceptionTest.php b/tests/Exception/Bulk/Response/ActionExceptionTest.php
index 4d3a45aa56..97059814b8 100644
--- a/tests/Exception/Bulk/Response/ActionExceptionTest.php
+++ b/tests/Exception/Bulk/Response/ActionExceptionTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Exception\Bulk\Response;
 
 use Elastica\Test\Exception\AbstractExceptionTest;
diff --git a/tests/Exception/Bulk/ResponseExceptionTest.php b/tests/Exception/Bulk/ResponseExceptionTest.php
index 3b5d6b3ecc..4e4df8b91e 100644
--- a/tests/Exception/Bulk/ResponseExceptionTest.php
+++ b/tests/Exception/Bulk/ResponseExceptionTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Exception\Bulk;
 
 use Elastica\Test\Exception\AbstractExceptionTest;
diff --git a/tests/Exception/BulkExceptionTest.php b/tests/Exception/BulkExceptionTest.php
index 703e2d87f6..38f8c23bf4 100644
--- a/tests/Exception/BulkExceptionTest.php
+++ b/tests/Exception/BulkExceptionTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Exception;
 
 /**
diff --git a/tests/Exception/ClientExceptionTest.php b/tests/Exception/ClientExceptionTest.php
index 95fe0c644d..8410ba83a2 100644
--- a/tests/Exception/ClientExceptionTest.php
+++ b/tests/Exception/ClientExceptionTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Exception;
 
 /**
diff --git a/tests/Exception/InvalidExceptionTest.php b/tests/Exception/InvalidExceptionTest.php
index b29732ef38..c7752116da 100644
--- a/tests/Exception/InvalidExceptionTest.php
+++ b/tests/Exception/InvalidExceptionTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Exception;
 
 /**
diff --git a/tests/Exception/NotFoundExceptionTest.php b/tests/Exception/NotFoundExceptionTest.php
index 4461729d5d..2fead75bbf 100644
--- a/tests/Exception/NotFoundExceptionTest.php
+++ b/tests/Exception/NotFoundExceptionTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Exception;
 
 /**
diff --git a/tests/Exception/NotImplementedExceptionTest.php b/tests/Exception/NotImplementedExceptionTest.php
index a8db701b64..890f3f2334 100644
--- a/tests/Exception/NotImplementedExceptionTest.php
+++ b/tests/Exception/NotImplementedExceptionTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Exception;
 
 use Elastica\Exception\NotImplementedException;
diff --git a/tests/Exception/QueryBuilderExceptionTest.php b/tests/Exception/QueryBuilderExceptionTest.php
index 168e766d89..91670f9c78 100644
--- a/tests/Exception/QueryBuilderExceptionTest.php
+++ b/tests/Exception/QueryBuilderExceptionTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Exception;
 
 /**
diff --git a/tests/Exception/RuntimeExceptionTest.php b/tests/Exception/RuntimeExceptionTest.php
index fd5c3cd5f7..b1980196e3 100644
--- a/tests/Exception/RuntimeExceptionTest.php
+++ b/tests/Exception/RuntimeExceptionTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Exception;
 
 /**
diff --git a/tests/Index/RecoveryTest.php b/tests/Index/RecoveryTest.php
index acc2e20358..a646fe10c3 100644
--- a/tests/Index/RecoveryTest.php
+++ b/tests/Index/RecoveryTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Index;
 
 use Elastica\Index\Recovery;
diff --git a/tests/Index/SettingsTest.php b/tests/Index/SettingsTest.php
index ce25e806ee..e3475d4a36 100644
--- a/tests/Index/SettingsTest.php
+++ b/tests/Index/SettingsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Index;
 
 use Elastic\Elasticsearch\Exception\ClientResponseException;
diff --git a/tests/Index/StatsTest.php b/tests/Index/StatsTest.php
index 85dce732a9..2e2874e9f0 100644
--- a/tests/Index/StatsTest.php
+++ b/tests/Index/StatsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Index;
 
 use Elastica\Index\Stats;
diff --git a/tests/IndexTemplateTest.php b/tests/IndexTemplateTest.php
index 6ccad10961..bd66de7878 100644
--- a/tests/IndexTemplateTest.php
+++ b/tests/IndexTemplateTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test;
 
 use Elastic\Elasticsearch\Exception\ClientResponseException;
diff --git a/tests/IndexTest.php b/tests/IndexTest.php
index 74effafbfd..11c0f8bf55 100644
--- a/tests/IndexTest.php
+++ b/tests/IndexTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test;
 
 use Elastic\Elasticsearch\Exception\ClientResponseException;
diff --git a/tests/JSONTest.php b/tests/JSONTest.php
index 4ba139d210..02d2668916 100644
--- a/tests/JSONTest.php
+++ b/tests/JSONTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test;
 
 use Elastica\JSON;
diff --git a/tests/MappingTest.php b/tests/MappingTest.php
index 79babfcf62..1f70565a34 100644
--- a/tests/MappingTest.php
+++ b/tests/MappingTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test;
 
 use Elastica\Document;
diff --git a/tests/Multi/MultiBuilderTest.php b/tests/Multi/MultiBuilderTest.php
index a3a77b30b3..5f64193096 100644
--- a/tests/Multi/MultiBuilderTest.php
+++ b/tests/Multi/MultiBuilderTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Multi;
 
 use Elastica\Multi\MultiBuilder;
diff --git a/tests/Multi/SearchTest.php b/tests/Multi/SearchTest.php
index edc51400fc..d59570a693 100644
--- a/tests/Multi/SearchTest.php
+++ b/tests/Multi/SearchTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Multi;
 
 use Elastica\Document;
diff --git a/tests/Node/InfoTest.php b/tests/Node/InfoTest.php
index 792fa23bcd..0ce429abb6 100644
--- a/tests/Node/InfoTest.php
+++ b/tests/Node/InfoTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Node;
 
 use Elastica\Node;
diff --git a/tests/NodeTest.php b/tests/NodeTest.php
index e039bb455e..1d1be7ab13 100644
--- a/tests/NodeTest.php
+++ b/tests/NodeTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test;
 
 use Elastica\Node;
diff --git a/tests/ParamTest.php b/tests/ParamTest.php
index 2cf04059cf..bd1668d453 100644
--- a/tests/ParamTest.php
+++ b/tests/ParamTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test;
 
 use Elastica\Exception\InvalidException;
diff --git a/tests/PipelineTest.php b/tests/PipelineTest.php
index b7b17e850b..c9ec96a9fd 100644
--- a/tests/PipelineTest.php
+++ b/tests/PipelineTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test;
 
 use Elastic\Elasticsearch\Exception\ClientResponseException;
diff --git a/tests/PointInTimeTest.php b/tests/PointInTimeTest.php
index 3320ea3035..822465e903 100644
--- a/tests/PointInTimeTest.php
+++ b/tests/PointInTimeTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test;
 
 use Elastica\Test\Base as BaseTest;
diff --git a/tests/Processor/AppendProcessorTest.php b/tests/Processor/AppendProcessorTest.php
index 5cb18761f3..e15cb87bea 100644
--- a/tests/Processor/AppendProcessorTest.php
+++ b/tests/Processor/AppendProcessorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Processor;
 
 use Elastica\Bulk;
diff --git a/tests/Processor/AttachmentProcessorTest.php b/tests/Processor/AttachmentProcessorTest.php
index d2851c6259..f76b48b7bf 100644
--- a/tests/Processor/AttachmentProcessorTest.php
+++ b/tests/Processor/AttachmentProcessorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Processor;
 
 use Elastica\Bulk;
diff --git a/tests/Processor/BytesProcessorTest.php b/tests/Processor/BytesProcessorTest.php
index 2e958427f3..0a36184c91 100644
--- a/tests/Processor/BytesProcessorTest.php
+++ b/tests/Processor/BytesProcessorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Processor;
 
 use Elastica\Processor\BytesProcessor;
diff --git a/tests/Processor/ConvertProcessorTest.php b/tests/Processor/ConvertProcessorTest.php
index 020e5dd74d..460a53856d 100644
--- a/tests/Processor/ConvertProcessorTest.php
+++ b/tests/Processor/ConvertProcessorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Processor;
 
 use Elastica\Bulk;
diff --git a/tests/Processor/DateIndexNameProcessorTest.php b/tests/Processor/DateIndexNameProcessorTest.php
index b626c382ec..5fbaff8308 100644
--- a/tests/Processor/DateIndexNameProcessorTest.php
+++ b/tests/Processor/DateIndexNameProcessorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Processor;
 
 use Elastica\Processor\DateIndexNameProcessor;
diff --git a/tests/Processor/DateProcessorTest.php b/tests/Processor/DateProcessorTest.php
index b55e366bf8..998d964612 100644
--- a/tests/Processor/DateProcessorTest.php
+++ b/tests/Processor/DateProcessorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Processor;
 
 use Elastica\Bulk;
diff --git a/tests/Processor/DotExpanderProcessorTest.php b/tests/Processor/DotExpanderProcessorTest.php
index 34827b2c12..33039b8ba6 100644
--- a/tests/Processor/DotExpanderProcessorTest.php
+++ b/tests/Processor/DotExpanderProcessorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Processor;
 
 use Elastica\Bulk;
diff --git a/tests/Processor/FailProcessorTest.php b/tests/Processor/FailProcessorTest.php
index 0e0190915b..bffd2cae5f 100644
--- a/tests/Processor/FailProcessorTest.php
+++ b/tests/Processor/FailProcessorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Processor;
 
 use Elastica\Bulk;
diff --git a/tests/Processor/ForeachProcessorTest.php b/tests/Processor/ForeachProcessorTest.php
index fff6a88680..95a0bc2510 100644
--- a/tests/Processor/ForeachProcessorTest.php
+++ b/tests/Processor/ForeachProcessorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Processor;
 
 use Elastica\Bulk;
diff --git a/tests/Processor/JoinProcessorTest.php b/tests/Processor/JoinProcessorTest.php
index 91c9b09429..5f7e50d06a 100644
--- a/tests/Processor/JoinProcessorTest.php
+++ b/tests/Processor/JoinProcessorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Processor;
 
 use Elastica\Bulk;
diff --git a/tests/Processor/JsonProcessorTest.php b/tests/Processor/JsonProcessorTest.php
index ea4acf1291..36555e600d 100644
--- a/tests/Processor/JsonProcessorTest.php
+++ b/tests/Processor/JsonProcessorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Processor;
 
 use Elastica\Bulk;
diff --git a/tests/Processor/KvProcessorTest.php b/tests/Processor/KvProcessorTest.php
index efbf176ceb..6a393fa572 100644
--- a/tests/Processor/KvProcessorTest.php
+++ b/tests/Processor/KvProcessorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Processor;
 
 use Elastica\Processor\KvProcessor;
diff --git a/tests/Processor/LowercaseProcessorTest.php b/tests/Processor/LowercaseProcessorTest.php
index 663db45e0f..158d268270 100644
--- a/tests/Processor/LowercaseProcessorTest.php
+++ b/tests/Processor/LowercaseProcessorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Processor;
 
 use Elastica\Bulk;
diff --git a/tests/Processor/RemoveProcessorTest.php b/tests/Processor/RemoveProcessorTest.php
index 0b7e4fda21..4c8fd05b3d 100644
--- a/tests/Processor/RemoveProcessorTest.php
+++ b/tests/Processor/RemoveProcessorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Processor;
 
 use Elastica\Bulk;
diff --git a/tests/Processor/RenameProcessorTest.php b/tests/Processor/RenameProcessorTest.php
index ad8846d998..6f7e26430e 100644
--- a/tests/Processor/RenameProcessorTest.php
+++ b/tests/Processor/RenameProcessorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Processor;
 
 use Elastica\Bulk;
diff --git a/tests/Processor/SetProcessorTest.php b/tests/Processor/SetProcessorTest.php
index 1585a28d52..bcddb236a8 100644
--- a/tests/Processor/SetProcessorTest.php
+++ b/tests/Processor/SetProcessorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Processor;
 
 use Elastica\Bulk;
diff --git a/tests/Processor/SortProcessorTest.php b/tests/Processor/SortProcessorTest.php
index 3f0bc02f40..1850158c45 100644
--- a/tests/Processor/SortProcessorTest.php
+++ b/tests/Processor/SortProcessorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Processor;
 
 use Elastica\Bulk;
diff --git a/tests/Processor/SplitProcessorTest.php b/tests/Processor/SplitProcessorTest.php
index b31bdc02c3..5a030d7ac6 100644
--- a/tests/Processor/SplitProcessorTest.php
+++ b/tests/Processor/SplitProcessorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Processor;
 
 use Elastica\Bulk;
diff --git a/tests/Processor/TrimProcessorTest.php b/tests/Processor/TrimProcessorTest.php
index b419ba59e0..3a4e9cb65d 100644
--- a/tests/Processor/TrimProcessorTest.php
+++ b/tests/Processor/TrimProcessorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Processor;
 
 use Elastica\Bulk;
diff --git a/tests/Processor/UppercaseProcessorTest.php b/tests/Processor/UppercaseProcessorTest.php
index 52792f5e47..ee6208b522 100644
--- a/tests/Processor/UppercaseProcessorTest.php
+++ b/tests/Processor/UppercaseProcessorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Processor;
 
 use Elastica\Bulk;
diff --git a/tests/Query/BoolQueryTest.php b/tests/Query/BoolQueryTest.php
index 5ae4603cc9..4bc04cc813 100644
--- a/tests/Query/BoolQueryTest.php
+++ b/tests/Query/BoolQueryTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Document;
diff --git a/tests/Query/BoostingTest.php b/tests/Query/BoostingTest.php
index b0c8b7d7fd..d0a846f089 100644
--- a/tests/Query/BoostingTest.php
+++ b/tests/Query/BoostingTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Query\Boosting;
diff --git a/tests/Query/CombinedFieldsQueryTest.php b/tests/Query/CombinedFieldsQueryTest.php
index 31567029d1..de775dac9b 100644
--- a/tests/Query/CombinedFieldsQueryTest.php
+++ b/tests/Query/CombinedFieldsQueryTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Document;
diff --git a/tests/Query/ConstantScoreTest.php b/tests/Query/ConstantScoreTest.php
index bad3883434..87a1986aab 100644
--- a/tests/Query/ConstantScoreTest.php
+++ b/tests/Query/ConstantScoreTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Query\ConstantScore;
diff --git a/tests/Query/DisMaxTest.php b/tests/Query/DisMaxTest.php
index 7c8d6c6df9..f84d27123d 100644
--- a/tests/Query/DisMaxTest.php
+++ b/tests/Query/DisMaxTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Document;
diff --git a/tests/Query/DistanceFeatureTest.php b/tests/Query/DistanceFeatureTest.php
index a22e6736bb..88b3ff8122 100644
--- a/tests/Query/DistanceFeatureTest.php
+++ b/tests/Query/DistanceFeatureTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Query\DistanceFeature;
diff --git a/tests/Query/EscapeStringTest.php b/tests/Query/EscapeStringTest.php
index 8a594345ca..2db43b5bc9 100644
--- a/tests/Query/EscapeStringTest.php
+++ b/tests/Query/EscapeStringTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Document;
diff --git a/tests/Query/ExistsTest.php b/tests/Query/ExistsTest.php
index 0e19ae86cc..842e265221 100644
--- a/tests/Query/ExistsTest.php
+++ b/tests/Query/ExistsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Query\Exists;
diff --git a/tests/Query/FunctionScoreTest.php b/tests/Query/FunctionScoreTest.php
index 0ac934cd04..daf25b9dc4 100644
--- a/tests/Query/FunctionScoreTest.php
+++ b/tests/Query/FunctionScoreTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Document;
diff --git a/tests/Query/FuzzyTest.php b/tests/Query/FuzzyTest.php
index 20138dc33f..9c19eafa44 100644
--- a/tests/Query/FuzzyTest.php
+++ b/tests/Query/FuzzyTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Document;
diff --git a/tests/Query/GeoBoundingBoxTest.php b/tests/Query/GeoBoundingBoxTest.php
index 9373e784c6..3f13b54478 100644
--- a/tests/Query/GeoBoundingBoxTest.php
+++ b/tests/Query/GeoBoundingBoxTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Exception\InvalidException;
diff --git a/tests/Query/GeoDistanceTest.php b/tests/Query/GeoDistanceTest.php
index 543a7471cd..2d699b24e9 100644
--- a/tests/Query/GeoDistanceTest.php
+++ b/tests/Query/GeoDistanceTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Document;
diff --git a/tests/Query/GeoPolygonTest.php b/tests/Query/GeoPolygonTest.php
index 30b6ad9190..513c678d8e 100644
--- a/tests/Query/GeoPolygonTest.php
+++ b/tests/Query/GeoPolygonTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Document;
diff --git a/tests/Query/GeoShapePreIndexedTest.php b/tests/Query/GeoShapePreIndexedTest.php
index 5363c3f4bc..df6fbc9619 100644
--- a/tests/Query/GeoShapePreIndexedTest.php
+++ b/tests/Query/GeoShapePreIndexedTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Document;
diff --git a/tests/Query/GeoShapeProvidedTest.php b/tests/Query/GeoShapeProvidedTest.php
index fd40ba0714..19c08cc4cf 100644
--- a/tests/Query/GeoShapeProvidedTest.php
+++ b/tests/Query/GeoShapeProvidedTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Document;
diff --git a/tests/Query/HasChildTest.php b/tests/Query/HasChildTest.php
index 66e1b4a721..63032a5208 100644
--- a/tests/Query/HasChildTest.php
+++ b/tests/Query/HasChildTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Mapping;
diff --git a/tests/Query/HasParentTest.php b/tests/Query/HasParentTest.php
index 4a25ae3161..72509e49c9 100644
--- a/tests/Query/HasParentTest.php
+++ b/tests/Query/HasParentTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Mapping;
diff --git a/tests/Query/HighlightTest.php b/tests/Query/HighlightTest.php
index 4118e954d7..d64ebb51b7 100644
--- a/tests/Query/HighlightTest.php
+++ b/tests/Query/HighlightTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Document;
diff --git a/tests/Query/IdsTest.php b/tests/Query/IdsTest.php
index 80a5338052..15c5d14804 100644
--- a/tests/Query/IdsTest.php
+++ b/tests/Query/IdsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Document;
diff --git a/tests/Query/InnerHitsTest.php b/tests/Query/InnerHitsTest.php
index 80fc24432e..d1efc52e8c 100644
--- a/tests/Query/InnerHitsTest.php
+++ b/tests/Query/InnerHitsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Index;
diff --git a/tests/Query/LimitTest.php b/tests/Query/LimitTest.php
index b9b729e9fa..4bf6c76d22 100644
--- a/tests/Query/LimitTest.php
+++ b/tests/Query/LimitTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Query\Limit;
diff --git a/tests/Query/MatchAllTest.php b/tests/Query/MatchAllTest.php
index 3a8f93c9c9..e2dc07fe88 100644
--- a/tests/Query/MatchAllTest.php
+++ b/tests/Query/MatchAllTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Document;
diff --git a/tests/Query/MatchNoneTest.php b/tests/Query/MatchNoneTest.php
index a1f893ec65..16b423b1c8 100644
--- a/tests/Query/MatchNoneTest.php
+++ b/tests/Query/MatchNoneTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Document;
diff --git a/tests/Query/MatchPhrasePrefixTest.php b/tests/Query/MatchPhrasePrefixTest.php
index 915ae3ae7d..d5b4299164 100644
--- a/tests/Query/MatchPhrasePrefixTest.php
+++ b/tests/Query/MatchPhrasePrefixTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Document;
diff --git a/tests/Query/MatchPhraseTest.php b/tests/Query/MatchPhraseTest.php
index 993024a710..d3934fc57e 100644
--- a/tests/Query/MatchPhraseTest.php
+++ b/tests/Query/MatchPhraseTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Document;
diff --git a/tests/Query/MatchQueryTest.php b/tests/Query/MatchQueryTest.php
index 736dca002f..a4e895f69a 100644
--- a/tests/Query/MatchQueryTest.php
+++ b/tests/Query/MatchQueryTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Document;
diff --git a/tests/Query/MoreLikeThisTest.php b/tests/Query/MoreLikeThisTest.php
index e7636ae3ad..a9cd4e7546 100644
--- a/tests/Query/MoreLikeThisTest.php
+++ b/tests/Query/MoreLikeThisTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Document;
diff --git a/tests/Query/MultiMatchTest.php b/tests/Query/MultiMatchTest.php
index 190cb456ea..a4b392e9da 100644
--- a/tests/Query/MultiMatchTest.php
+++ b/tests/Query/MultiMatchTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Document;
diff --git a/tests/Query/NestedTest.php b/tests/Query/NestedTest.php
index 58e399c3c3..a8be50babd 100644
--- a/tests/Query/NestedTest.php
+++ b/tests/Query/NestedTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Query\Nested;
diff --git a/tests/Query/ParentIdTest.php b/tests/Query/ParentIdTest.php
index bb8ab58958..18804d9a45 100644
--- a/tests/Query/ParentIdTest.php
+++ b/tests/Query/ParentIdTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Mapping;
diff --git a/tests/Query/PercolateTest.php b/tests/Query/PercolateTest.php
index c8ba2d8292..0600cb4c58 100644
--- a/tests/Query/PercolateTest.php
+++ b/tests/Query/PercolateTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Client;
diff --git a/tests/Query/PostFilterTest.php b/tests/Query/PostFilterTest.php
index 2fdbb6d5f9..d8349226b0 100644
--- a/tests/Query/PostFilterTest.php
+++ b/tests/Query/PostFilterTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Document;
diff --git a/tests/Query/PrefixTest.php b/tests/Query/PrefixTest.php
index 4e538d7f5e..3efe28e8da 100644
--- a/tests/Query/PrefixTest.php
+++ b/tests/Query/PrefixTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Query\Prefix;
diff --git a/tests/Query/QueryStringTest.php b/tests/Query/QueryStringTest.php
index afdce8dc64..9324f0a3fd 100644
--- a/tests/Query/QueryStringTest.php
+++ b/tests/Query/QueryStringTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastic\Elasticsearch\Exception\ClientResponseException;
@@ -28,7 +30,7 @@ public function testSearchMultipleFields(): void
         $this->assertEquals(['query_string' => $expected], $query->toArray());
 
         $fields = [];
-        $max = \mt_rand(1, 10);
+        $max = \random_int(1, 10);
         for ($i = 0; $i < $max; ++$i) {
             $fields[] = \uniqid();
         }
diff --git a/tests/Query/RangeTest.php b/tests/Query/RangeTest.php
index 71320a7efa..f687b4cf19 100644
--- a/tests/Query/RangeTest.php
+++ b/tests/Query/RangeTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Document;
diff --git a/tests/Query/RegexpTest.php b/tests/Query/RegexpTest.php
index 11e8e2fe7c..1689a4dd70 100644
--- a/tests/Query/RegexpTest.php
+++ b/tests/Query/RegexpTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Query\Regexp;
diff --git a/tests/Query/RescoreTest.php b/tests/Query/RescoreTest.php
index e85f1e1631..2e435f03b1 100644
--- a/tests/Query/RescoreTest.php
+++ b/tests/Query/RescoreTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Query;
diff --git a/tests/Query/ScriptTest.php b/tests/Query/ScriptTest.php
index 27d03b93ee..64c31f7e00 100644
--- a/tests/Query/ScriptTest.php
+++ b/tests/Query/ScriptTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Query\Script as ScriptQuery;
diff --git a/tests/Query/SimpleQueryStringTest.php b/tests/Query/SimpleQueryStringTest.php
index 08cb117cd3..b6b37dd34e 100644
--- a/tests/Query/SimpleQueryStringTest.php
+++ b/tests/Query/SimpleQueryStringTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Document;
diff --git a/tests/Query/SimpleTest.php b/tests/Query/SimpleTest.php
index a48a65453a..d6b80be844 100644
--- a/tests/Query/SimpleTest.php
+++ b/tests/Query/SimpleTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Query\Simple;
diff --git a/tests/Query/SpanContainingTest.php b/tests/Query/SpanContainingTest.php
index bca03a2258..91fc816b54 100644
--- a/tests/Query/SpanContainingTest.php
+++ b/tests/Query/SpanContainingTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Document;
diff --git a/tests/Query/SpanFirstTest.php b/tests/Query/SpanFirstTest.php
index de6a011083..b280919e90 100644
--- a/tests/Query/SpanFirstTest.php
+++ b/tests/Query/SpanFirstTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Document;
diff --git a/tests/Query/SpanMultiTest.php b/tests/Query/SpanMultiTest.php
index 439b1c9f17..0b2c2bdfad 100644
--- a/tests/Query/SpanMultiTest.php
+++ b/tests/Query/SpanMultiTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Document;
diff --git a/tests/Query/SpanNearTest.php b/tests/Query/SpanNearTest.php
index 20fe390191..c522c0870f 100644
--- a/tests/Query/SpanNearTest.php
+++ b/tests/Query/SpanNearTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Document;
diff --git a/tests/Query/SpanNotTest.php b/tests/Query/SpanNotTest.php
index 7dca223595..73f0a434b0 100644
--- a/tests/Query/SpanNotTest.php
+++ b/tests/Query/SpanNotTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Document;
diff --git a/tests/Query/SpanOrTest.php b/tests/Query/SpanOrTest.php
index 74564009d3..7a32b635e8 100644
--- a/tests/Query/SpanOrTest.php
+++ b/tests/Query/SpanOrTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Document;
diff --git a/tests/Query/SpanTermTest.php b/tests/Query/SpanTermTest.php
index 1a48ae9eb4..faddc13fa1 100644
--- a/tests/Query/SpanTermTest.php
+++ b/tests/Query/SpanTermTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Document;
diff --git a/tests/Query/SpanWithinTest.php b/tests/Query/SpanWithinTest.php
index 8c10532ac4..05afae7251 100644
--- a/tests/Query/SpanWithinTest.php
+++ b/tests/Query/SpanWithinTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Document;
diff --git a/tests/Query/TermTest.php b/tests/Query/TermTest.php
index 1b8db6b8fa..3655c42017 100644
--- a/tests/Query/TermTest.php
+++ b/tests/Query/TermTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Query\Term;
diff --git a/tests/Query/TermsSetTest.php b/tests/Query/TermsSetTest.php
index 97d538dfef..7b377427c2 100644
--- a/tests/Query/TermsSetTest.php
+++ b/tests/Query/TermsSetTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Document;
diff --git a/tests/Query/TermsTest.php b/tests/Query/TermsTest.php
index aa0b58a63f..6c6bc0a113 100644
--- a/tests/Query/TermsTest.php
+++ b/tests/Query/TermsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Document;
diff --git a/tests/Query/WildcardTest.php b/tests/Query/WildcardTest.php
index 0d789b7046..a4d1558cef 100644
--- a/tests/Query/WildcardTest.php
+++ b/tests/Query/WildcardTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Query;
 
 use Elastica\Document;
diff --git a/tests/QueryBuilder/DSL/AbstractDSLTest.php b/tests/QueryBuilder/DSL/AbstractDSLTest.php
index 6cc8afcc29..179fd515b5 100644
--- a/tests/QueryBuilder/DSL/AbstractDSLTest.php
+++ b/tests/QueryBuilder/DSL/AbstractDSLTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\QueryBuilder\DSL;
 
 use Elastica\Exception\NotImplementedException;
@@ -20,7 +22,7 @@ protected function _assertImplemented(DSL $dsl, string $methodName, string $clas
 
         // Check method signature
         $class = new \ReflectionClass($className);
-        $method = new \ReflectionMethod(\get_class($dsl), $methodName);
+        $method = new \ReflectionMethod($dsl::class, $methodName);
         if (!$class->hasMethod('__construct')) {
             $this->assertEmpty($method->getParameters(), 'Constructor is not defined, but method has some parameters');
         } else {
diff --git a/tests/QueryBuilder/DSL/AggregationTest.php b/tests/QueryBuilder/DSL/AggregationTest.php
index a00b792852..5dd9fa4c63 100644
--- a/tests/QueryBuilder/DSL/AggregationTest.php
+++ b/tests/QueryBuilder/DSL/AggregationTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\QueryBuilder\DSL;
 
 use Elastica\Aggregation;
diff --git a/tests/QueryBuilder/DSL/CollapseTest.php b/tests/QueryBuilder/DSL/CollapseTest.php
index 0d4fb64107..d627162054 100644
--- a/tests/QueryBuilder/DSL/CollapseTest.php
+++ b/tests/QueryBuilder/DSL/CollapseTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\QueryBuilder\DSL;
 
 use Elastica\Collapse;
diff --git a/tests/QueryBuilder/DSL/QueryTest.php b/tests/QueryBuilder/DSL/QueryTest.php
index cbe713ecfb..6ad7795b19 100644
--- a/tests/QueryBuilder/DSL/QueryTest.php
+++ b/tests/QueryBuilder/DSL/QueryTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\QueryBuilder\DSL;
 
 use Elastica\Query;
diff --git a/tests/QueryBuilder/DSL/SuggestTest.php b/tests/QueryBuilder/DSL/SuggestTest.php
index cc323d4772..d208aed4e9 100644
--- a/tests/QueryBuilder/DSL/SuggestTest.php
+++ b/tests/QueryBuilder/DSL/SuggestTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\QueryBuilder\DSL;
 
 use Elastica\QueryBuilder\DSL;
diff --git a/tests/QueryBuilder/VersionTest.php b/tests/QueryBuilder/VersionTest.php
index 7cd8272624..6384a53434 100644
--- a/tests/QueryBuilder/VersionTest.php
+++ b/tests/QueryBuilder/VersionTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\QueryBuilder;
 
 use Elastica\QueryBuilder\DSL;
@@ -37,28 +39,28 @@ private function assertVersions(Version $version, array $dsl): void
         foreach ($version->getQueries() as $query) {
             $this->assertTrue(
                 \method_exists($dsl[0], $query),
-                'query "'.$query.'" in '.\get_class($version).' must be defined in '.\get_class($dsl[0])
+                'query "'.$query.'" in '.$version::class.' must be defined in '.\get_class($dsl[0])
             );
         }
 
         foreach ($version->getAggregations() as $aggregation) {
             $this->assertTrue(
                 \method_exists($dsl[1], $aggregation),
-                'aggregation "'.$aggregation.'" in '.\get_class($version).' must be defined in '.\get_class($dsl[2])
+                'aggregation "'.$aggregation.'" in '.$version::class.' must be defined in '.\get_class($dsl[2])
             );
         }
 
         foreach ($version->getSuggesters() as $suggester) {
             $this->assertTrue(
                 \method_exists($dsl[2], $suggester),
-                'suggester "'.$suggester.'" in '.\get_class($version).' must be defined in '.\get_class($dsl[2])
+                'suggester "'.$suggester.'" in '.$version::class.' must be defined in '.\get_class($dsl[2])
             );
         }
 
         foreach ($version->getCollapsers() as $collapser) {
             $this->assertTrue(
                 \method_exists($dsl[3], $collapser),
-                'suggester "'.$collapser.'" in '.\get_class($version).' must be defined in '.\get_class($dsl[3])
+                'suggester "'.$collapser.'" in '.$version::class.' must be defined in '.\get_class($dsl[3])
             );
         }
     }
diff --git a/tests/QueryBuilderTest.php b/tests/QueryBuilderTest.php
index ba0660e078..f7d0d28a79 100644
--- a/tests/QueryBuilderTest.php
+++ b/tests/QueryBuilderTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test;
 
 use Elastica\Aggregation\AbstractAggregation;
diff --git a/tests/QueryTest.php b/tests/QueryTest.php
index 6f8c0db0b6..6818e7c876 100644
--- a/tests/QueryTest.php
+++ b/tests/QueryTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test;
 
 use Elastica\Aggregation\Terms as TermsAggregation;
diff --git a/tests/ReindexTest.php b/tests/ReindexTest.php
index 2e933df0b3..0d8f843168 100644
--- a/tests/ReindexTest.php
+++ b/tests/ReindexTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test;
 
 use Elastic\Elasticsearch\Exception\ClientResponseException;
diff --git a/tests/ResponseFunctionalTest.php b/tests/ResponseFunctionalTest.php
index 1d8ec28ef2..934f7dbce3 100644
--- a/tests/ResponseFunctionalTest.php
+++ b/tests/ResponseFunctionalTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test;
 
 use Elastica\Document;
diff --git a/tests/ResponseTest.php b/tests/ResponseTest.php
index 04422f8241..8888c0a190 100644
--- a/tests/ResponseTest.php
+++ b/tests/ResponseTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test;
 
 use Elastica\Response;
diff --git a/tests/ResultSet/BuilderTest.php b/tests/ResultSet/BuilderTest.php
index d696b031dc..6c4307dd6c 100644
--- a/tests/ResultSet/BuilderTest.php
+++ b/tests/ResultSet/BuilderTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\ResultSet;
 
 use Elastica\Query;
diff --git a/tests/ResultSet/ChainProcessorTest.php b/tests/ResultSet/ChainProcessorTest.php
index 474a524edc..f89dddf09f 100644
--- a/tests/ResultSet/ChainProcessorTest.php
+++ b/tests/ResultSet/ChainProcessorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\ResultSet;
 
 use Elastica\Query;
diff --git a/tests/ResultSet/ProcessingBuilderTest.php b/tests/ResultSet/ProcessingBuilderTest.php
index 2cb2e6e1d2..fc44b16511 100644
--- a/tests/ResultSet/ProcessingBuilderTest.php
+++ b/tests/ResultSet/ProcessingBuilderTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\ResultSet;
 
 use Elastica\Query;
diff --git a/tests/ResultSetTest.php b/tests/ResultSetTest.php
index a2f724ad83..c733e0a2a5 100644
--- a/tests/ResultSetTest.php
+++ b/tests/ResultSetTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test;
 
 use Elastica\Document;
diff --git a/tests/ResultTest.php b/tests/ResultTest.php
index 81a0588f36..b35e85996c 100644
--- a/tests/ResultTest.php
+++ b/tests/ResultTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test;
 
 use Elastica\Document;
diff --git a/tests/Script/ScriptFieldsTest.php b/tests/Script/ScriptFieldsTest.php
index afd7f2ea6f..3e195f94c3 100644
--- a/tests/Script/ScriptFieldsTest.php
+++ b/tests/Script/ScriptFieldsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Script;
 
 use Elastica\Mapping;
diff --git a/tests/Script/ScriptIdTest.php b/tests/Script/ScriptIdTest.php
index 118f8730cd..1f12ad011f 100644
--- a/tests/Script/ScriptIdTest.php
+++ b/tests/Script/ScriptIdTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Script;
 
 use Elastica\Exception\InvalidException;
diff --git a/tests/Script/ScriptTest.php b/tests/Script/ScriptTest.php
index d20950c618..b94efbe79d 100644
--- a/tests/Script/ScriptTest.php
+++ b/tests/Script/ScriptTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Script;
 
 use Elastica\Exception\InvalidException;
diff --git a/tests/ScrollTest.php b/tests/ScrollTest.php
index 3123f3880b..f7a678cdc6 100644
--- a/tests/ScrollTest.php
+++ b/tests/ScrollTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test;
 
 use Elastica\Client;
diff --git a/tests/SearchTest.php b/tests/SearchTest.php
index dcaa143662..e21147ff0e 100644
--- a/tests/SearchTest.php
+++ b/tests/SearchTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test;
 
 use Elastic\Elasticsearch\Exception\ClientResponseException;
diff --git a/tests/SnapshotTest.php b/tests/SnapshotTest.php
index 6a6169da7f..2082e102f2 100644
--- a/tests/SnapshotTest.php
+++ b/tests/SnapshotTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test;
 
 use Elastica\Document;
diff --git a/tests/StatusTest.php b/tests/StatusTest.php
index dced6609e9..dc7cab0206 100644
--- a/tests/StatusTest.php
+++ b/tests/StatusTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test;
 
 use Elastic\Elasticsearch\Exception\ClientResponseException;
@@ -96,9 +98,7 @@ public function testAliasExists(): void
 
         $indicesWithAlias = $status->getIndicesWithAlias($aliasName);
         $this->assertEquals([$indexName], \array_map(
-            static function ($index) {
-                return $index->getName();
-            },
+            static fn ($index) => $index->getName(),
             $indicesWithAlias
         ));
     }
diff --git a/tests/Suggest/CompletionTest.php b/tests/Suggest/CompletionTest.php
index 58df78ee97..7833319fdb 100644
--- a/tests/Suggest/CompletionTest.php
+++ b/tests/Suggest/CompletionTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Suggest;
 
 use Elastica\Document;
diff --git a/tests/Suggest/PhraseTest.php b/tests/Suggest/PhraseTest.php
index 65b621ae1a..af091f1a24 100644
--- a/tests/Suggest/PhraseTest.php
+++ b/tests/Suggest/PhraseTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Suggest;
 
 use Elastica\Document;
diff --git a/tests/Suggest/TermTest.php b/tests/Suggest/TermTest.php
index 57a7fdadf3..c573a5bfee 100644
--- a/tests/Suggest/TermTest.php
+++ b/tests/Suggest/TermTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test\Suggest;
 
 use Elastica\Document;
diff --git a/tests/SuggestTest.php b/tests/SuggestTest.php
index 5e50bebe06..f6648128a3 100644
--- a/tests/SuggestTest.php
+++ b/tests/SuggestTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test;
 
 use Elastica\Exception\NotImplementedException;
diff --git a/tests/TaskTest.php b/tests/TaskTest.php
index ab4117c56d..fc26a9d8e3 100644
--- a/tests/TaskTest.php
+++ b/tests/TaskTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test;
 
 use Elastica\Document;
diff --git a/tests/UtilTest.php b/tests/UtilTest.php
index 27106a72d7..a2e5c4f7a8 100644
--- a/tests/UtilTest.php
+++ b/tests/UtilTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Elastica\Test;
 
 use Elastica\Test\Base as BaseTest;
diff --git a/tests/bootstrap.php b/tests/bootstrap.php
index dcdcefbf97..7b64d8ac10 100644
--- a/tests/bootstrap.php
+++ b/tests/bootstrap.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // normalize ES_VERSION for version_compare
 if (isset($_SERVER['ES_VERSION']) && \str_contains($_SERVER['ES_VERSION'], 'SNAPSHOT')) {
     $_SERVER['ES_VERSION'] = \str_replace('-SNAPSHOT', '', $_SERVER['ES_VERSION']);