Lazy fixtures in PyTest - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a lazy fixture in pytest?

A lazy fixture is a fixture that is not executed immediately but only when it is actually used in a test. It helps to delay setup until necessary, saving time and resources.

beginner

How do you declare a lazy fixture in pytest?

You declare a lazy fixture by using the @pytest.fixture decorator with scope and optionally autouse=False. The fixture code runs only when a test requests it.

intermediate

Why use lazy fixtures instead of eager fixtures?

Lazy fixtures run only when needed, which saves test execution time and avoids unnecessary setup. Eager fixtures run before every test regardless of need, which can slow tests down.

beginner

What happens if a lazy fixture is not used in any test?

If a lazy fixture is not used by any test, it will not run at all. This means no setup or teardown code inside it will execute, saving resources.

intermediate

Can lazy fixtures depend on other fixtures in pytest?

Yes, lazy fixtures can depend on other fixtures. The dependent fixtures will also be lazy and run only when needed by the test.

What triggers a lazy fixture to run in pytest?

A Before any test runs automatically

B When the fixture is declared

C When pytest starts

D When a test function requests it as a parameter

Lazy fixtures run only when a test function includes them as parameters.

Which decorator is used to create a lazy fixture in pytest?

A @pytest.fixture

B @pytest.test

C @pytest.lazy

D @pytest.setup

The @pytest.fixture decorator creates fixtures, which are lazy by default unless autouse=True.

If a fixture is marked with autouse=True, is it lazy?

A No, it runs before every test automatically

B No, it never runs

C Yes, but only for some tests

D Yes, it runs only when requested

Fixtures with autouse=True run automatically before each test, so they are not lazy.

What is a benefit of using lazy fixtures?

A They run faster because they run before all tests

B They reduce test time by running only when needed

C They run multiple times per test

D They replace test functions

Lazy fixtures save time by running only when a test actually uses them.

Can a lazy fixture depend on another fixture?

A Only if both are autouse

B No, fixtures cannot depend on each other

C Yes, dependencies are also lazy

D Only if declared in the same file

Fixtures can depend on other fixtures, and those dependencies are lazy too.

Explain what lazy fixtures are in pytest and why they are useful.

Think about when the fixture code runs during testing.

Describe how fixture dependencies work with lazy fixtures in pytest.

Consider how pytest manages fixture calls.