Test discovery rules in PyTest - Test Execution Trace

Test Overview

This test checks how pytest discovers test functions in a file based on naming conventions. It verifies that only functions starting with test_ are executed as tests.

Test Code - pytest

PyTest

import pytest

def test_addition():
    assert 1 + 1 == 2

def addition_test():
    assert 2 + 2 == 4

def test_subtraction():
    assert 5 - 3 == 2

class TestMathOperations:
    def test_multiplication(self):
        assert 3 * 3 == 9
    
    def multiplication_test(self):
        assert 4 * 4 == 16

if __name__ == "__main__":
    pytest.main(["-v"])

Execution Trace - 7 Steps

Step	Action	System State	Assertion	Result
1	Test runner starts and scans the test file for test functions and classes	pytest identifies functions and classes matching discovery rules	Functions starting with 'test_' and classes starting with 'Test' are selected	PASS
2	pytest runs function 'test_addition'	Function 'test_addition' executes	assert 1 + 1 == 2	PASS
3	pytest skips function 'addition_test' because it does not start with 'test_'	Function 'addition_test' is not executed	-	PASS
4	pytest runs function 'test_subtraction'	Function 'test_subtraction' executes	assert 5 - 3 == 2	PASS
5	pytest finds class 'TestMathOperations' and runs its method 'test_multiplication'	Method 'test_multiplication' executes	assert 3 * 3 == 9	PASS
6	pytest skips method 'multiplication_test' because it does not start with 'test_'	Method 'multiplication_test' is not executed	-	PASS
7	Test run completes with all discovered tests passed	pytest reports 3 tests run, 0 failed, 0 skipped	-	PASS

Failure Scenario

Failing Condition: A test function named incorrectly (not starting with 'test_') is expected to run but is skipped

Execution Trace Quiz - 3 Questions

Which function will pytest run as a test?

A addition_test

B test_addition

C multiplication_test

D all functions

Key Result

pytest discovers tests by looking for functions and methods starting with 'test_' and classes starting with 'Test'. Naming tests correctly is essential for them to run.