Checking membership (in, not in) in PyTest - Build an Automation Script

Verify membership of elements in a list using 'in' and 'not in'

Preconditions (2)

Step 1: Create a list named 'fruits' containing ['apple', 'banana', 'cherry']

Step 2: Check if 'banana' is in the list 'fruits'

Step 3: Check if 'orange' is not in the list 'fruits'

Step 4: Assert that 'banana' is found in the list

Step 5: Assert that 'orange' is not found in the list

✅ Expected Result: The test passes confirming 'banana' is in the list and 'orange' is not in the list

Automation Requirements - pytest

Assertions Needed:

Assert 'banana' in fruits

Assert 'orange' not in fruits

Best Practices:

Use clear and descriptive test function names

Use assert statements directly for membership checks

Keep test code simple and readable

Automated Solution

PyTest

import pytest

def test_membership_in_list():
    fruits = ['apple', 'banana', 'cherry']
    # Check if 'banana' is in the list
    assert 'banana' in fruits, "Expected 'banana' to be in the fruits list"
    # Check if 'orange' is not in the list
    assert 'orange' not in fruits, "Expected 'orange' to not be in the fruits list"

This test function test_membership_in_list creates a list called fruits with three items.

It uses assert statements to check membership:

• 'banana' in fruits confirms 'banana' is present.
• 'orange' not in fruits confirms 'orange' is absent.

If either assertion fails, pytest will show a clear message explaining what was expected.

This keeps the test simple, readable, and easy to maintain.

Common Mistakes - 3 Pitfalls

{'mistake': "Using '==' to check membership instead of 'in'", 'why_bad': 'It only compares one element, not membership in a collection', 'correct_approach': "Use 'in' keyword to check if an element exists in a list or collection"}

Not providing assertion messages

Checking membership on wrong variable or empty list

Bonus Challenge

Now add data-driven testing with 3 different fruits lists and check membership for 'banana' and 'orange'

Show Hint