Fixture dependencies (fixture using fixture) in PyTest - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a fixture dependency in pytest?

A fixture dependency happens when one fixture uses another fixture to set up its environment. This means one fixture can call another fixture to reuse setup code.

beginner

How do you make a fixture use another fixture in pytest?

You add the other fixture as a parameter to your fixture function. Pytest will automatically run the dependent fixture first and pass its result.

beginner

Example: What does this code do?

@pytest.fixture
def db():
    return "database connection"

@pytest.fixture
def user(db):
    return f"user with {db}"

The 'user' fixture depends on the 'db' fixture. When 'user' runs, pytest first runs 'db' and passes its result. So 'user' returns 'user with database connection'.

beginner

Why use fixture dependencies?

Fixture dependencies help avoid repeating setup code. They make tests cleaner and easier to maintain by reusing common setup steps.

intermediate

What happens if a fixture dependency fails?

If a fixture that another fixture depends on fails, pytest will stop and mark the test as failed or error because the setup is incomplete.

How do you declare that one fixture depends on another in pytest?

A By adding the dependent fixture as a parameter to the fixture function

B By calling the fixture inside the test function

C By importing the fixture inside the test file

D By using a special decorator @depends

In pytest, you declare fixture dependencies by listing the other fixture as a parameter in your fixture function.

What will pytest do if a fixture dependency fails during setup?

A Mark the test as failed or error

B Run the test anyway

C Ignore the failure and continue

D Skip the test silently

If a fixture dependency fails, pytest stops the test and marks it as failed or error because the setup is incomplete.

Why is using fixture dependencies beneficial?

A It makes tests slower

B It avoids repeating setup code and improves maintainability

C It hides test failures

D It makes tests harder to read

Fixture dependencies help reuse setup code, making tests cleaner and easier to maintain.

In this code, what is the output of the 'user' fixture?

@pytest.fixture
def db():
    return "db connection"

@pytest.fixture
def user(db):
    return f"user with {db}"

A "user"

B "db connection"

C "user with db connection"

D Error

The 'user' fixture uses the 'db' fixture and returns 'user with db connection'.

How does pytest know the order to run fixtures with dependencies?

A It runs all fixtures in parallel

B It runs fixtures randomly

C It runs fixtures alphabetically

D It runs dependent fixtures first before the fixtures that use them

Pytest runs fixtures that are dependencies first, then passes their results to the fixtures that depend on them.

Explain how fixture dependencies work in pytest and why they are useful.

Think about how one setup step can build on another.

Describe what happens when a fixture that another fixture depends on fails during test setup.

Consider the chain reaction of failures in setup.