pytest框架中的前置后置条件

### pytest Framework Setup and Teardown Methods In the context of `pytest`, setup and teardown methods are used to define actions that should be executed before or after tests. These mechanisms ensure that each test runs in an isolated environment, preventing side effects from one test affecting others. #### Using Fixtures for Setup and Teardown `pytest` provides fixtures as a powerful mechanism for managing setup and teardown operations. A fixture is defined using the `@pytest.fixture` decorator, and it can perform initialization (setup) when requested by a test function and cleanup (teardown) once the test completes[^1]. Here is an example demonstrating how to use fixtures: ```python import pytest @pytest.fixture def resource_setup(): print("\nSetup called.") yield "Resource" print("\nTeardown called.") def test_example(resource_setup): print(f"\nTest running with {resource_setup}.") assert True ``` The above code defines a fixture named `resource_setup`. The `yield` statement separates the setup phase (before yielding) from the teardown phase (after yielding). When the test concludes, the teardown logic executes automatically[^2]. #### Class-Level Setup and Teardown For scenarios where you need class-level setup and teardown, you can combine fixtures with scope parameters. By setting the `scope="class"` argument within the `@pytest.fixture` decorator, the same fixture instance will persist across all methods inside a single test class[^3]: ```python import pytest @pytest.fixture(scope="class") def class_resource_setup(request): request.cls.resource = "Class Resource" print("\nClass level setup.") yield print("\nClass level teardown.") @pytest.mark.usefixtures("class_resource_setup") class TestExample: def test_one(self): print(f"\nTest One uses {self.resource}.") assert self.resource == "Class Resource" def test_two(self): print(f"\nTest Two also uses {self.resource}.") assert self.resource == "Class Resource" ``` This ensures both `test_one` and `test_two` share the same setup while executing their respective assertions independently[^4]. #### Module and Session Scopes Fixtures support broader scopes such as module (`scope="module"`) or session (`scope="session"`), which execute only once per module or entire test suite respectively. This reduces redundant setups during large-scale testing sessions but requires careful handling due to shared states between multiple tests[^3]. ---