Fixture composition in PyTest - Build an Automation Script

Test fixture composition with pytest fixtures

Preconditions (2)

Step 1: Create a fixture named 'db_connection' that returns a string 'db_connected'

Step 2: Create another fixture named 'user' that depends on 'db_connection' fixture and returns 'user_from_' concatenated with the db_connection value

Step 3: Write a test function that uses the 'user' fixture

Step 4: Inside the test, assert that the 'user' fixture value equals 'user_from_db_connected'

✅ Expected Result: The test passes confirming that fixture composition works correctly

Automation Requirements - pytest

Assertions Needed:

Assert that the composed fixture returns the expected combined string

Best Practices:

Use pytest fixtures with proper scope

Use fixture dependency injection by passing fixtures as function arguments

Keep fixtures simple and composable

Automated Solution

PyTest

import pytest

@pytest.fixture
def db_connection():
    return 'db_connected'

@pytest.fixture
def user(db_connection):
    return f'user_from_{db_connection}'

def test_user_fixture(user):
    assert user == 'user_from_db_connected'

The db_connection fixture returns a simple string representing a database connection.

The user fixture depends on db_connection by accepting it as a parameter. It composes a new string using the value from db_connection.

The test function test_user_fixture uses the user fixture and asserts that the returned value matches the expected composed string.

This shows how pytest fixtures can be composed by passing one fixture into another, making tests modular and reusable.

Common Mistakes - 3 Pitfalls

Not passing dependent fixture as a parameter to the fixture function

Using print statements instead of assertions in tests

Defining fixtures inside test functions

Bonus Challenge

Now add data-driven testing with 3 different db_connection values and verify the composed user fixture for each.

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