pytest.raises context manager - Test Execution Trace

Test Overview

This test checks that a function raises a ValueError when given invalid input. It uses pytest.raises as a context manager to catch the exception and verify it happens as expected.

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 str(exc_info.value) == "Cannot divide by zero"

Execution Trace - 5 Steps

Step	Action	System State	Assertion	Result
1	Test starts	pytest test runner initialized	-	PASS
2	Calls divide(10, 0) inside pytest.raises context manager	Function divide is called with a=10, b=0	-	PASS
3	divide function raises ValueError("Cannot divide by zero")	Exception ValueError is raised	pytest.raises catches ValueError	PASS
4	Assertion checks exception message equals "Cannot divide by zero"	Exception info stored in exc_info	assert str(exc_info.value) == "Cannot divide by zero"	PASS
5	Test ends successfully	No errors, test passed	-	PASS

Failure Scenario

Failing Condition: divide does not raise ValueError when dividing by zero

Execution Trace Quiz - 3 Questions

What does pytest.raises do in this test?

A It logs the exception without failing the test

B It prevents the function from running

C It catches the expected exception to verify it was raised

D It retries the function until no exception occurs

Key Result

Using pytest.raises as a context manager lets you verify that specific exceptions are raised and also inspect their details, making your tests precise and clear.