@pytest.mark.parametrize decorator - Build an Automation Script

Test addition function with multiple inputs using @pytest.mark.parametrize

Preconditions (3)

Step 1: Create a test function named test_add that takes two inputs and an expected output

Step 2: Use @pytest.mark.parametrize to provide three sets of inputs and expected outputs: (1, 2, 3), (5, 5, 10), (0, 0, 0)

Step 3: Inside the test function, call the addition function with the two inputs

Step 4: Assert that the result equals the expected output

✅ Expected Result: The test runs three times with different inputs and all assertions pass

Automation Requirements - pytest

Assertions Needed:

Assert the addition function output equals the expected result for each input set

Best Practices:

Use @pytest.mark.parametrize to avoid repeating test code

Name test function clearly

Keep test data simple and readable

Automated Solution

PyTest

import pytest

def add(a: int, b: int) -> int:
    return a + b

@pytest.mark.parametrize("a,b,expected", [
    (1, 2, 3),
    (5, 5, 10),
    (0, 0, 0)
])
def test_add(a, b, expected):
    result = add(a, b)
    assert result == expected, f"Expected {expected} but got {result}"

This code defines a simple addition function add.

The @pytest.mark.parametrize decorator runs the test_add function three times with different inputs and expected outputs.

Inside the test, it calls add with the inputs and checks if the result matches the expected value.

This way, we test multiple cases without writing separate test functions.

Common Mistakes - 3 Pitfalls

Not using @pytest.mark.parametrize and writing separate test functions for each input

Incorrect parameter names in the decorator string and function signature mismatch

Using complex or unclear test data inside parametrize

Bonus Challenge

Now add data-driven testing with 3 different inputs including negative numbers and zero

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