Avoiding test interdependence in PyTest - Build an Automation Script

Verify independent test execution in pytest

Preconditions (2)

Step 1: Create two test functions: test_add and test_subtract

Step 2: In test_add, call add(2, 3) and verify the result is 5

Step 3: In test_subtract, call subtract(5, 3) and verify the result is 2

Step 4: Run tests individually and together to ensure no test depends on another

✅ Expected Result: Both tests pass independently with no shared state or order dependency

Automation Requirements - pytest

Assertions Needed:

assert add(2, 3) == 5

assert subtract(5, 3) == 2

Best Practices:

Use fresh state for each test

Avoid sharing variables or state between tests

Do not rely on test execution order

Use fixtures with scope='function' if setup is needed

Automated Solution

PyTest

import pytest

# Simple calculator functions
def add(a, b):
    return a + b

def subtract(a, b):
    return a - b

# Test functions

def test_add():
    result = add(2, 3)
    assert result == 5

def test_subtract():
    result = subtract(5, 3)
    assert result == 2

This test script defines two simple functions: add and subtract. Each test function calls one of these and asserts the expected result.

Each test is independent: they do not share variables or state. This means you can run test_add or test_subtract alone or together in any order, and they will pass.

This avoids test interdependence, which is important because tests that depend on each other can cause confusing failures and make debugging hard.

Common Mistakes - 3 Pitfalls

Sharing variables between tests

Relying on test execution order

Using global state without reset

Bonus Challenge

Now add data-driven testing with 3 different input pairs for add and subtract functions

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