diff --git a/tests/unit/test_config.py b/tests/unit/test_config.py
new file mode 100644
index 0000000..eb4a82d
--- /dev/null
+++ b/tests/unit/test_config.py
@@ -0,0 +1,114 @@
+"""Tests for configuration."""
+
+import os
+import tempfile
+from pathlib import Path
+
+import pytest
+import yaml
+
+from mockapi.core.config import Config, load_config
+
+
+class TestConfig:
+    """Test cases for Config."""
+
+    def test_default_values(self):
+        """Test default configuration values."""
+        config = Config()
+        assert config.port == 8080
+        assert config.host == "0.0.0.0"
+        assert config.delay == 0
+        assert config.random_delay is False
+        assert config.seed == 42
+        assert config.validate_requests is True
+        assert config.validate_responses is False
+        assert config.strict_validation is False
+
+    def test_load_from_dict(self):
+        """Test creating config with dict values."""
+        config = Config(
+            port=3000,
+            host="127.0.0.1",
+            delay=100,
+            seed=123,
+        )
+        assert config.port == 3000
+        assert config.host == "127.0.0.1"
+        assert config.delay == 100
+        assert config.seed == 123
+
+    def test_to_dict(self):
+        """Test converting config to dictionary."""
+        config = Config(port=9000, host="localhost")
+        d = config.to_dict()
+        assert d["port"] == 9000
+        assert d["host"] == "localhost"
+        assert "delay" in d
+        assert "seed" in d
+
+    def test_load_from_env(self):
+        """Test loading config from environment variables."""
+        os.environ["MOCKAPI_PORT"] = "5000"
+        os.environ["MOCKAPI_HOST"] = "127.0.0.1"
+        os.environ["MOCKAPI_SEED"] = "999"
+
+        config = load_config()
+
+        assert config.port == 5000
+        assert config.host == "127.0.0.1"
+        assert config.seed == 999
+
+        del os.environ["MOCKAPI_PORT"]
+        del os.environ["MOCKAPI_HOST"]
+        del os.environ["MOCKAPI_SEED"]
+
+    def test_load_from_file(self):
+        """Test loading config from YAML file."""
+        config_data = {
+            "port": 7000,
+            "host": "0.0.0.0",
+            "delay": 200,
+            "random_delay": True,
+            "seed": 456,
+        }
+
+        with tempfile.NamedTemporaryFile(
+            mode="w", suffix=".yaml", delete=False
+        ) as f:
+            yaml.dump(config_data, f)
+            temp_path = f.name
+
+        try:
+            config = load_config(temp_path)
+            assert config.port == 7000
+            assert config.host == "0.0.0.0"
+            assert config.delay == 200
+            assert config.random_delay is True
+            assert config.seed == 456
+        finally:
+            os.unlink(temp_path)
+
+    def test_env_overrides_file(self):
+        """Test that environment variables override file config."""
+        config_data = {"port": 7000, "host": "0.0.0.0"}
+
+        with tempfile.NamedTemporaryFile(
+            mode="w", suffix=".yaml", delete=False
+        ) as f:
+            yaml.dump(config_data, f)
+            temp_path = f.name
+
+        os.environ["MOCKAPI_PORT"] = "9000"
+
+        try:
+            config = load_config(temp_path)
+            assert config.port == 9000
+        finally:
+            os.unlink(temp_path)
+            del os.environ["MOCKAPI_PORT"]
+
+    def test_load_config_default_path(self):
+        """Test load_config with no arguments."""
+        config = load_config()
+        assert isinstance(config, Config)