Given-When-Then pattern in PyTest - Test Execution Trace

Test Overview

This test uses the Given-When-Then pattern to check if a simple calculator adds two numbers correctly. It verifies that the sum is as expected.

Test Code - pytest

PyTest

import pytest

class Calculator:
    def add(self, a, b):
        return a + b

@pytest.fixture
def calculator():
    # Given: a calculator instance
    return Calculator()

def test_addition(calculator):
    # When: adding two numbers
    result = calculator.add(3, 4)
    # Then: the result should be 7
    assert result == 7, f"Expected 7 but got {result}"

Execution Trace - 3 Steps

Step	Action	System State	Assertion	Result
1	Test starts and pytest fixture creates a Calculator instance	Calculator object is ready for use	-	PASS
2	Calls add method with inputs 3 and 4	Calculator adds 3 + 4 internally	-	PASS
3	Checks if the result equals 7	Result is 7	assert result == 7	PASS

Failure Scenario

Failing Condition: The add method returns a wrong sum, e.g., 8 instead of 7

Execution Trace Quiz - 3 Questions

What does the 'Given' step represent in this test?

A Setting up the calculator instance

B Performing the addition

C Checking the result

D Cleaning up after the test

Key Result

Using the Given-When-Then pattern helps organize tests clearly by separating setup, action, and verification steps, making tests easier to read and maintain.