Test modules in PyTest - Test Execution Trace

Test Overview

This test module contains two simple test functions to verify basic arithmetic operations. It checks if addition and multiplication work as expected.

Test Code - pytest

PyTest

import pytest

def test_addition():
    result = 2 + 3
    assert result == 5

def test_multiplication():
    result = 4 * 5
    assert result == 20

Execution Trace - 6 Steps

Step	Action	System State	Assertion	Result
1	Pytest starts test discovery and finds test_addition function	Test module loaded with two test functions	—	PASS
2	test_addition function runs: calculates 2 + 3	Calculation result stored in variable	Assert that result == 5	PASS
3	test_addition completes successfully	Test passed	—	PASS
4	Pytest runs test_multiplication function: calculates 4 * 5	Calculation result stored in variable	Assert that result == 20	PASS
5	test_multiplication completes successfully	Test passed	—	PASS
6	Pytest finishes running all tests in the module	All tests passed	—	PASS

Failure Scenario

Failing Condition: If an assertion fails, for example if result != expected value

Execution Trace Quiz - 3 Questions

What does the test_addition function verify?

A That 2 + 3 equals 6

B That 2 + 3 equals 5

C That 4 * 5 equals 20

D That 4 * 5 equals 25

Key Result

Organize related tests into modules with clear, simple test functions to keep tests easy to read and maintain.

Practice

1. What is the correct way to name a Python file so that pytest recognizes it as a test module?

easy

A. The file name can be anything as long as it contains tests.

B. The file name should start with check_.

C. The file name should be pytest_module.py.

D. The file name should start with test_ or end with _test.py.

Solution

1. Step 1: Understand pytest file naming conventions

   pytest automatically discovers test files if their names start with test_ or end with _test.py.

2. Step 2: Evaluate each option

   Only The file name should start with test_ or end with _test.py. matches the correct naming pattern for pytest to find test modules automatically.

3. Final Answer:

   The file name should start with test_ or end with _test.py. -> Option D

4. Quick Check:

   pytest test file naming = start with test_ or end with _test.py [OK]

Hint: Remember test files start with test_ or end with _test.py [OK]

Common Mistakes:

• Assuming any file with tests is recognized
• Using incorrect prefixes like check_
• Naming files without .py extension

2. Which of the following is the correct syntax for a test function inside a pytest test module?

easy

A. def test_function():

B. def check_function():

C. def function_test():

D. def testing_function():

Solution

1. Step 1: Recall pytest test function naming rules

   pytest runs functions that start with test_ automatically as tests.

2. Step 2: Match options with naming rule

   Only def test_function(): defines a function starting with test_, so pytest will recognize it as a test.

3. Final Answer:

   def test_function(): -> Option A

4. Quick Check:

   Test functions start with test_ [OK]

Hint: Test functions must start with test_ to run automatically [OK]

Common Mistakes:

• Naming test functions without test_ prefix
• Using other prefixes like check_ or testing_
• Forgetting to define functions with def

3. Given the following test module test_sample.py with these functions:

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

def add():
    return 1 + 1

def test_subtract():
    assert 2 - 1 == 1

Which functions will pytest run as tests?

medium

A. All three functions

B. Only add

C. test_add and test_subtract

D. Only test_add

Solution

1. Step 1: Identify pytest test function naming

   pytest runs functions starting with test_ automatically as tests.

2. Step 2: Check each function name

   test_add and test_subtract start with test_, so pytest runs them. add does not start with test_, so it is ignored.

3. Final Answer:

   test_add and test_subtract -> Option C

4. Quick Check:

   Functions starting with test_ run as tests [OK]

Hint: Only functions starting with test_ run as tests [OK]

Common Mistakes:

• Thinking all functions in test file run as tests
• Confusing helper functions with test functions
• Ignoring function name prefixes

4. You have a test module named test_math.py with this code:

def test_multiply():
    assert 2 * 3 == 5

When you run pytest, what will happen?

medium

A. The test will fail because the assertion is incorrect.

B. pytest will not find any tests to run.

C. pytest will skip the test because of a syntax error.

D. The test will pass because 2 * 3 equals 6.

Solution

1. Step 1: Analyze the assertion in test_multiply

   The assertion checks if 2 * 3 == 5, which is false because 2 * 3 equals 6.

2. Step 2: Understand pytest test result

   pytest runs the test and finds the assertion false, so the test fails.

3. Final Answer:

   The test will fail because the assertion is incorrect. -> Option A

4. Quick Check:

   False assertion causes test failure [OK]

Hint: Check if assertion condition is true or false [OK]

Common Mistakes:

• Assuming test passes despite wrong assertion
• Confusing syntax errors with assertion failures
• Thinking pytest skips failing tests

5. You want to organize tests for a calculator app. You create two files: test_add.py and test_subtract.py. Each file has multiple test functions starting with test_. How does pytest handle these test modules when you run pytest in the folder?

hard

A. pytest requires you to specify each test module to run tests.

B. pytest runs all test functions from both modules automatically.

C. pytest runs only tests from the first module alphabetically.

D. pytest runs tests only if you import modules manually.

Solution

1. Step 1: Understand pytest test discovery

   pytest automatically finds all test modules named with test_ prefix and runs all test functions inside them.

2. Step 2: Apply to multiple test modules

   When running pytest in the folder, it collects tests from both test_add.py and test_subtract.py and runs all test functions starting with test_.

3. Final Answer:

   pytest runs all test functions from both modules automatically. -> Option B

4. Quick Check:

   pytest auto-discovers all test modules and functions [OK]

Hint: pytest runs all test_ modules and functions in folder automatically [OK]

Common Mistakes:

• Thinking pytest runs only one module at a time
• Believing manual imports are needed for tests
• Assuming tests must be specified explicitly