Deterministic tests in PyTest - Build an Automation Script

Verify deterministic behavior of a function that returns a fixed output

Preconditions (2)

Step 1: Create a function named get_fixed_value that always returns the integer 42

Step 2: Write a pytest test function named test_get_fixed_value

Step 3: Call get_fixed_value inside the test

Step 4: Assert that the returned value is exactly 42

✅ Expected Result: The test passes every time with the value 42 returned and assertion successful

Automation Requirements - pytest

Assertions Needed:

Assert returned value equals 42

Best Practices:

Use clear function and test names

Keep tests independent and repeatable

Avoid randomness or external dependencies in the function

Automated Solution

PyTest

import pytest

def get_fixed_value():
    return 42


def test_get_fixed_value():
    result = get_fixed_value()
    assert result == 42, f"Expected 42 but got {result}"

The get_fixed_value function always returns 42, making it deterministic.

The test test_get_fixed_value calls this function and asserts the result is 42.

This ensures the test will pass every time, showing deterministic behavior.

Assertions include a helpful message if the test fails.

Common Mistakes - 3 Pitfalls

Using random or time-based values inside the function

Not asserting the exact expected value

Writing tests that depend on external state or files

Bonus Challenge

Now add data-driven testing with 3 different fixed values returned by separate functions

Show Hint