capsys for capturing output in PyTest - Test Execution Trace

Test Overview

This test checks if the function prints the expected message to the console. It uses capsys to capture the printed output and verifies it matches the expected string.

Test Code - pytest

PyTest

import pytest

def greet(name):
    print(f"Hello, {name}!")

def test_greet_output(capsys):
    greet("Alice")
    captured = capsys.readouterr()
    assert captured.out == "Hello, Alice!\n"

Execution Trace - 5 Steps

Step	Action	System State	Assertion	Result
1	Test starts	pytest test runner initialized	-	PASS
2	Calls greet("Alice") function	Function prints 'Hello, Alice!' to standard output	-	PASS
3	capsys.readouterr() captures printed output	Captured output contains 'Hello, Alice!\n'	-	PASS
4	Assert captured.out equals 'Hello, Alice!\n'	Captured output matches expected string	assert captured.out == 'Hello, Alice!\n'	PASS
5	Test ends	Test passed with no errors	-	PASS

Failure Scenario

Failing Condition: The function prints a different message or no message at all

Execution Trace Quiz - 3 Questions

What does capsys.readouterr() do in this test?

A Checks if the output matches expected string

B Runs the test function

C Captures the printed output from the function

D Raises an error if output is missing

Key Result

Use capsys in pytest to capture and verify printed output easily, ensuring your functions produce the expected console messages.