Arrange-Act-Assert pattern in PyTest - Test Execution Trace

Test Overview

This test uses the Arrange-Act-Assert pattern to check if the add function correctly adds two numbers. It arranges the inputs, acts by calling the function, and asserts the expected result.

Test Code - pytest

PyTest

import pytest

def add(a, b):
    return a + b

def test_add_two_numbers():
    # Arrange
    num1 = 3
    num2 = 5
    expected_sum = 8

    # Act
    result = add(num1, num2)

    # Assert
    assert result == expected_sum, f"Expected {expected_sum} but got {result}"

Execution Trace - 5 Steps

Step	Action	System State	Assertion	Result
1	Test starts	pytest test runner initialized	-	PASS
2	Arrange inputs: num1=3, num2=5, expected_sum=8	Variables set in test function	-	PASS
3	Act by calling add(num1, num2)	Function add called with arguments 3 and 5	-	PASS
4	Assert that result equals expected_sum	Result is 8, expected_sum is 8	assert 8 == 8	PASS
5	Test ends	Test passed with no errors	-	PASS

Failure Scenario

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

Execution Trace Quiz - 3 Questions

What is the purpose of the 'Arrange' step in this test?

A Call the function being tested

B Set up the inputs and expected results

C Check if the test passed

D Clean up after the test

Key Result

Using the Arrange-Act-Assert pattern helps keep tests clear and easy to understand by separating setup, action, and verification steps.