Checking exception attributes in PyTest - Test Execution Trace

Test Overview

This test checks that a function raises a ValueError with the correct message when given invalid input.

Test Code - pytest

PyTest

import pytest

def divide(a, b):
    if b == 0:
        raise ValueError("Cannot divide by zero")
    return a / b

def test_divide_by_zero():
    with pytest.raises(ValueError) as exc_info:
        divide(10, 0)
    assert exc_info.value.args[0] == "Cannot divide by zero"

Execution Trace - 6 Steps

Step	Action	System State	Assertion	Result
1	Test starts	Test runner is ready to execute test_divide_by_zero	-	PASS
2	Calls divide(10, 0)	Function divide is executing with a=10, b=0	-	PASS
3	Raises ValueError with message 'Cannot divide by zero'	Exception is raised inside divide function	-	PASS
4	pytest.raises context captures the ValueError as exc_info	Exception info stored in exc_info variable	-	PASS
5	Assert exc_info.value.args[0] equals 'Cannot divide by zero'	Checking exception message content	Exception message is exactly 'Cannot divide by zero'	PASS
6	Test ends successfully	Test passed with no errors	-	PASS

Failure Scenario

Failing Condition: The divide function does not raise ValueError or raises with wrong message

Execution Trace Quiz - 3 Questions

What does the test check about the exception?

A The exception type and its message content

B Only that an exception is raised, no message check

C That no exception is raised

D The exception stack trace

Key Result

Always check both the type and the message of exceptions to ensure your code fails as expected with clear error information.