test: add minimum sum algorithm test

Rf #6

spec/algorithms_ruby/minimum_sum_spec.rb

@@ -1,10 +1,25 @@
 # frozen_string_literal: true
 
 RSpec.describe AlgorithmsRuby::MinimumSum do
-  context ".call" do
-    let(:arr) { [2, 4, 1, 3] }
-    subject { described_class.call(arr) }
+  let(:array) { [2, 4, 1, 3] }
+  subject { described_class.new(array) }
 
-    it { expect(subject).to eq(3) }
+  describe ".call" do
+    it "returns the correct minimum sum" do
+      expect(subject.call).to eq(3)
+    end
+  end
+
+  describe "#minimum_value" do
+    it "returns the minimum value" do
+      expect(subject.send(:minimum_value)).to eq(1)
+    end
+  end
+
+  describe "#repetitions" do
+    it "returns the correct number of repetitions" do
+      expect(subject.send(:repetitions)).to eq(3)
+    end
   end
 end
+