Approximate comparisons (pytest.approx) - Test Execution Trace

Test Overview

This test checks if a floating-point calculation result is approximately equal to an expected value using pytest.approx. It verifies that small differences due to floating-point precision do not cause the test to fail.

Test Code - pytest

PyTest

import pytest

def test_approximate_comparison():
    result = 0.1 + 0.2
    expected = 0.3
    assert result == pytest.approx(expected, rel=1e-9)

Execution Trace - 5 Steps

Step	Action	System State	Assertion	Result
1	Test starts	pytest test runner initialized	-	PASS
2	Calls test_approximate_comparison function	Function execution begins	-	PASS
3	Calculates result = 0.1 + 0.2	result variable holds floating-point sum 0.30000000000000004	-	PASS
4	Compares result to expected using pytest.approx with relative tolerance 1e-9	Comparison allows small floating-point difference	Assert result == pytest.approx(expected, rel=1e-9)	PASS
5	Test completes successfully	Test runner reports test passed	-	PASS

Failure Scenario

Failing Condition: The relative tolerance is set too low, causing the small floating-point difference to fail the comparison

Execution Trace Quiz - 3 Questions

What does pytest.approx help with in this test?

A Checks if two strings are exactly equal

B Skips the test if values differ

C Allows comparison of floating-point numbers with a tolerance

D Converts numbers to integers before comparing

Key Result

Use pytest.approx to compare floating-point numbers approximately, avoiding false test failures caused by tiny precision differences.