Deterministic tests in PyTest - Test Execution Trace

Test Overview

This test checks that a function returns the same output every time it is called with the same input. It verifies the test is deterministic, meaning it does not depend on random or changing data.

Test Code - pytest

PyTest

import pytest

def add_five(x):
    return x + 5

def test_add_five_deterministic():
    result1 = add_five(10)
    result2 = add_five(10)
    assert result1 == result2
    assert result1 == 15

Execution Trace - 6 Steps

Step	Action	System State	Assertion	Result
1	Test starts	pytest test runner initialized	-	PASS
2	Calls add_five(10) first time	Function add_five executes with input 10	No assertion yet	PASS
3	Calls add_five(10) second time	Function add_five executes again with input 10	No assertion yet	PASS
4	Assert result1 equals result2	Both results are 15	assert 15 == 15	PASS
5	Assert result1 equals 15	result1 is 15	assert 15 == 15	PASS
6	Test ends successfully	All assertions passed	-	PASS

Failure Scenario

Failing Condition: Function add_five returns different results for the same input

Execution Trace Quiz - 3 Questions

What does the test verify about the function add_five?

A It modifies the input value

B It returns random numbers

C It always returns the same output for the same input

D It raises an error for input 10

Key Result

Deterministic tests ensure functions produce consistent results for the same inputs, making tests reliable and easy to debug.