diff --git a/.tests/conftest.py b/.tests/conftest.py
new file mode 100644
index 0000000..88bb80b
--- /dev/null
+++ b/.tests/conftest.py
@@ -0,0 +1,161 @@
+"""Pytest configuration and fixtures for OpenAPI Mock Server tests."""
+
+import sys
+from pathlib import Path
+
+import pytest
+
+sys.path.insert(0, str(Path(__file__).parent.parent / "src"))
+
+
+@pytest.fixture
+def sample_openapi_spec():
+    """Sample OpenAPI 3.0 specification for testing."""
+    return {
+        "openapi": "3.0.0",
+        "info": {
+            "title": "Test API",
+            "version": "1.0.0",
+            "description": "A test API for unit tests"
+        },
+        "paths": {
+            "/users": {
+                "get": {
+                    "summary": "List users",
+                    "operationId": "listUsers",
+                    "responses": {
+                        "200": {
+                            "description": "A list of users",
+                            "content": {
+                                "application/json": {
+                                    "schema": {
+                                        "type": "array",
+                                        "items": {"$ref": "#/components/schemas/User"}
+                                    }
+                                }
+                            }
+                        }
+                    }
+                },
+                "post": {
+                    "summary": "Create user",
+                    "operationId": "createUser",
+                    "requestBody": {
+                        "content": {
+                            "application/json": {
+                                "schema": {"$ref": "#/components/schemas/User"}
+                            }
+                        }
+                    },
+                    "responses": {
+                        "201": {
+                            "description": "User created",
+                            "content": {
+                                "application/json": {
+                                    "schema": {"$ref": "#/components/schemas/User"}
+                                }
+                            }
+                        }
+                    }
+                }
+            },
+            "/users/{userId}": {
+                "get": {
+                    "summary": "Get user by ID",
+                    "operationId": "getUser",
+                    "parameters": [
+                        {
+                            "name": "userId",
+                            "in": "path",
+                            "required": True,
+                            "schema": {"type": "integer"}
+                        }
+                    ],
+                    "responses": {
+                        "200": {
+                            "description": "User found",
+                            "content": {
+                                "application/json": {
+                                    "schema": {"$ref": "#/components/schemas/User"}
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+        },
+        "components": {
+            "schemas": {
+                "User": {
+                    "type": "object",
+                    "required": ["id", "username", "email"],
+                    "properties": {
+                        "id": {"type": "integer", "format": "int64"},
+                        "username": {"type": "string", "minLength": 3, "maxLength": 50},
+                        "email": {"type": "string", "format": "email"},
+                        "created_at": {"type": "string", "format": "date-time"},
+                        "active": {"type": "boolean", "default": True}
+                    }
+                }
+            }
+        }
+    }
+
+
+@pytest.fixture
+def swagger_2_spec():
+    """Sample Swagger 2.0 specification for testing."""
+    return {
+        "swagger": "2.0",
+        "info": {
+            "title": "Swagger Test API",
+            "version": "2.0.0"
+        },
+        "paths": {
+            "/pets": {
+                "get": {
+                    "summary": "List pets",
+                    "operationId": "listPets",
+                    "responses": {
+                        "200": {
+                            "description": "A list of pets",
+                            "schema": {
+                                "type": "array",
+                                "items": {"$ref": "#/definitions/Pet"}
+                            }
+                        }
+                    }
+                }
+            }
+        },
+        "definitions": {
+            "Pet": {
+                "type": "object",
+                "required": ["id", "name"],
+                "properties": {
+                    "id": {"type": "integer"},
+                    "name": {"type": "string"},
+                    "tag": {"type": "string"}
+                }
+            }
+        }
+    }
+
+
+@pytest.fixture
+def temp_spec_file(tmp_path, sample_openapi_spec):
+    """Create a temporary OpenAPI spec file."""
+    import yaml
+    spec_path = tmp_path / "test-spec.yaml"
+    with open(spec_path, "w") as f:
+        yaml.dump(sample_openapi_spec, f)
+    return str(spec_path)
+
+
+@pytest.fixture
+def invalid_yaml_file(tmp_path):
+    """Create an invalid YAML file."""
+    file_path = tmp_path / "invalid.yaml"
+    with open(file_path, "w") as f:
+        f.write("invalid: yaml: content: [")
+    return str(file_path)