Test classes in PyTest - Test Execution Trace

Test Overview

This test class groups two simple tests that check basic math operations. It verifies that addition and multiplication work as expected.

Test Code - pytest

PyTest

import pytest

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

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

Execution Trace - 4 Steps

Step	Action	System State	Assertion	Result
1	Pytest starts and discovers the test class TestMathOperations	Test runner is ready to execute tests	—	PASS
2	Pytest runs test_addition method	Inside test_addition, result is calculated as 2 + 3	Assert that result == 5	PASS
3	Pytest runs test_multiplication method	Inside test_multiplication, result is calculated as 4 * 5	Assert that result == 20	PASS
4	Pytest finishes running all tests in TestMathOperations	All tests passed	—	PASS

Failure Scenario

Failing Condition: If the assertion in test_addition fails because result is not 5

Execution Trace Quiz - 3 Questions

What does the test_addition method verify?

A That 2 minus 3 equals -1

B That 2 plus 3 equals 5

C That 4 times 5 equals 20

D That 5 divided by 2 equals 2.5

Key Result

Using test classes helps organize related tests, making the test suite easier to read and maintain.

Practice

1. What is the main purpose of using test classes in pytest?

easy

A. To avoid writing assertions

B. To group related tests for better organization

C. To make tests run faster

D. To skip tests automatically

Solution

1. Step 1: Understand test grouping

   Test classes help organize related test functions together in one place.

2. Step 2: Recognize benefits

   This grouping improves readability and allows shared setup for tests.

3. Final Answer:

   To group related tests for better organization -> Option B

4. Quick Check:

   Test classes group tests = C [OK]

Hint: Test classes group related tests logically [OK]

Common Mistakes:

• Thinking test classes speed up tests
• Believing test classes skip tests
• Assuming test classes remove need for assertions

2. Which of the following is the correct way to name a pytest test class?

easy

A. class testExample:

B. class ExampleTest:

C. class TestExample:

D. class exampleTest:

Solution

1. Step 1: Recall pytest naming rules

   Pytest requires test classes to start with 'Test' exactly.

2. Step 2: Check options

   Only 'TestExample' starts with 'Test' correctly and follows naming conventions.

3. Final Answer:

   class TestExample: -> Option C

4. Quick Check:

   Class name starts with 'Test' = D [OK]

Hint: Test classes must start with 'Test' exactly [OK]

Common Mistakes:

• Starting class name with lowercase 'test'
• Placing 'Test' at the end of class name
• Using mixed case that doesn't start with 'Test'

3. Given the code below, what will pytest report when running these tests?

class TestMath:
    def test_add(self):
        assert 1 + 1 == 2

    def test_subtract(self):
        assert 5 - 3 == 1

medium

A. 1 test passed, 1 test failed

B. 2 tests passed

C. 2 tests failed

D. Syntax error, tests won't run

Solution

1. Step 1: Check each assertion

   test_add asserts 1+1==2 which is True; test_subtract asserts 5-3==1 which is False.

2. Step 2: Determine test results

   One test passes (test_add), one test fails (test_subtract).

3. Final Answer:

   1 test passed, 1 test failed -> Option A

4. Quick Check:

   Assertions true/false = 1 pass, 1 fail [OK]

Hint: Check each assertion result carefully [OK]

Common Mistakes:

• Assuming both tests pass without checking assertions
• Ignoring that 5 - 3 != 1
• Thinking syntax error due to indentation

4. Identify the error in the following pytest test class:

class TestCalc:
    def test_multiply(self):
        assert 2 * 3 == 6
    
    def multiply_test(self):
        assert 4 * 5 == 20

medium

A. Method 'multiply_test' will not be recognized as a test

B. Class name must not start with 'Test'

C. Missing assert statement in 'test_multiply'

D. Indentation error in method definitions

Solution

1. Step 1: Check method naming rules

   Pytest requires test methods to start with 'test_'. 'multiply_test' does not.

2. Step 2: Understand consequences

   Method 'multiply_test' will be ignored by pytest and not run as a test.

3. Final Answer:

   Method 'multiply_test' will not be recognized as a test -> Option A

4. Quick Check:

   Test methods start with 'test_' = A [OK]

Hint: Test methods must start with 'test_' [OK]

Common Mistakes:

• Thinking class name can't start with 'Test'
• Missing assert in test method
• Assuming indentation error without evidence

5. How can you share setup code for all tests inside a pytest test class?

hard

A. Define a method named 'setup_method' inside the class

B. Use a global variable outside the class

C. Write setup code inside each test method separately

D. Define a method named 'setup_class' inside the class

Solution

1. Step 1: Understand pytest setup methods

   Pytest supports 'setup_class' to run setup once for all tests in a class.

2. Step 2: Compare options

   'setup_method' runs before each test method, not once for all; global variables and repeated code are not best practice.

3. Final Answer:

   Define a method named 'setup_class' inside the class -> Option D

4. Quick Check:

   Class-wide setup uses 'setup_class' = B [OK]

Hint: Use 'setup_class' for one-time class setup [OK]

Common Mistakes:

• Confusing 'setup_method' with class-wide setup
• Using global variables instead of setup methods
• Repeating setup code in every test method