diff --git a/tests/ut/conftest.py b/tests/ut/conftest.py
index 876296f..e6cf0dd 100644
--- a/tests/ut/conftest.py
+++ b/tests/ut/conftest.py
@@ -1,4 +1,5 @@
 import logging
+import os
 import random
 from pathlib import Path
 
@@ -14,10 +15,6 @@
 logger = logging.getLogger(__name__)
 
 
-def pytest_addoption(parser: pytest.Parser) -> None:
-    parser.addoption("--region", default="us-east-1")
-
-
 def pytest_configure(config: pytest.Config) -> None:
     # Avoid overly verbose logging.
     logging.getLogger("boto3").setLevel(logging.INFO)
@@ -28,6 +25,13 @@ def pytest_configure(config: pytest.Config) -> None:
 
 @pytest.fixture(scope="session", autouse=True)
 def moto_server() -> MotoServer:
+    # Refer to http://docs.getmoto.org/en/latest/docs/getting_started.html#example-on-usage
+    os.environ["AWS_ACCESS_KEY_ID"] = "testing"
+    os.environ["AWS_SECRET_ACCESS_KEY"] = "testing"
+    os.environ["AWS_SECURITY_TOKEN"] = "testing"
+    os.environ["AWS_SESSION_TOKEN"] = "testing"
+    os.environ["AWS_DEFAULT_REGION"] = "us-east-1"
+
     for i, port in enumerate(random.sample(range(50000, 50500), 100)):
         try:
             server = MotoServer(ThreadedMotoServer(port=port))
@@ -43,24 +47,18 @@ def moto_server() -> MotoServer:
 
 @pytest.fixture(scope="session")
 def ec2(
-    request: pytest.FixtureRequest, moto_server: MotoServer,
+    request: pytest.FixtureRequest,
+    moto_server: MotoServer,
 ) -> EC2ServiceResource:
-    return boto3.resource(
-        "ec2",
-        endpoint_url=moto_server.endpoint,
-        region_name=request.config.getoption("--region"),
-    )
+    return boto3.resource("ec2", endpoint_url=moto_server.endpoint)
 
 
 @pytest.fixture(scope="session")
 def iam(
-    request: pytest.FixtureRequest, moto_server: MotoServer,
+    request: pytest.FixtureRequest,
+    moto_server: MotoServer,
 ) -> IAMServiceResource:
-    return boto3.resource(
-        "iam",
-        endpoint_url=moto_server.endpoint,
-        region_name=request.config.getoption("--region"),
-    )
+    return boto3.resource("iam", endpoint_url=moto_server.endpoint)
 
 
 @pytest.fixture(scope="session")
@@ -70,10 +68,7 @@ def this_dir() -> Path:
 
 @pytest.fixture(scope="module")
 def eks_client(
-    request: pytest.FixtureRequest, moto_server: MotoServer,
+    request: pytest.FixtureRequest,
+    moto_server: MotoServer,
 ) -> EKSClient:
-    return boto3.client(
-        "eks",
-        endpoint_url=moto_server.endpoint,
-        region_name=request.config.getoption("--region"),
-    )
+    return boto3.client("eks", endpoint_url=moto_server.endpoint)