Checking identity (is, is not) in PyTest - Test Execution Trace

Test Overview

This test checks if two variables point to the exact same object in memory using is and is not operators. It verifies identity, not just equality.

Test Code - pytest

PyTest

import pytest

def test_identity():
    a = [1, 2, 3]
    b = a
    c = [1, 2, 3]

    # Check that a and b are the same object
    assert a is b

    # Check that a and c are not the same object
    assert a is not c

    # Check that a and c have equal content
    assert a == c

Execution Trace - 8 Steps

Step	Action	System State	Assertion	Result
1	Test starts	pytest test runner initialized	-	PASS
2	Assign list [1, 2, 3] to variable a	Variable a points to a list object in memory	-	PASS
3	Assign variable b to reference the same object as a	Variables a and b point to the same list object	-	PASS
4	Assign variable c to a new list [1, 2, 3]	Variable c points to a different list object with same content	-	PASS
5	Assert that a is b (identity check)	a and b reference the same object	assert a is b	PASS
6	Assert that a is not c (identity check)	a and c reference different objects	assert a is not c	PASS
7	Assert that a == c (equality check)	a and c have equal content	assert a == c	PASS
8	Test ends	All assertions passed	-	PASS

Failure Scenario

Failing Condition: If the assertion 'assert a is b' fails because a and b do not reference the same object

Execution Trace Quiz - 3 Questions

What does the assertion 'assert a is b' verify in this test?

A That a and b are different objects

B That a and b have the same content

C That a and b point to the exact same object in memory

D That a and b are both lists

Key Result

Use 'is' and 'is not' to check if two variables point to the exact same object, not just if they look equal. This helps catch bugs where object identity matters.