Test classes in PyTest - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of pytest test class with setup method

What is the output when running this pytest test class?

PyTest

import pytest

class TestExample:
    def setup_method(self):
        self.value = 5

    def test_add(self):
        assert self.value + 3 == 8

    def test_subtract(self):
        assert self.value - 2 == 3

A Both tests fail

B test_add passes, test_subtract fails

C test_add fails, test_subtract passes

D Both tests pass

💡 Hint

setup_method runs before each test method to set self.value

The setup_method sets self.value to 5 before each test. test_add checks 5 + 3 == 8 which is True. test_subtract checks 5 - 2 == 3 which is True. So both tests pass.

❓ assertion

intermediate

Correct assertion to check list length in test class

Which assertion correctly checks that the list has exactly 4 items inside a pytest test method?

PyTest

class TestList:
    def test_length(self):
        items = [1, 2, 3, 4]

A assert items.count == 4

B assert items.length == 4

C assert len(items) == 4

D assert items.size() == 4

💡 Hint

Use Python's built-in function to get length of a list

len(items) returns the number of elements in the list. The other options use invalid syntax or methods not available on Python lists.

🔧 Debug

advanced

Identify the error in this pytest test class

What error will occur when running this pytest test class?

PyTest

class TestCalc:
    def setup(self):
        self.num = 10

    def test_multiply(self):
        assert self.num * 2 == 20

A AttributeError: 'TestCalc' object has no attribute 'num'

B AssertionError because 10 * 2 != 20

C No error, test passes

D SyntaxError due to missing colon

💡 Hint

Check if the setup method is named correctly for pytest

pytest expects setup_method(self) or setup_class(cls) for setup. The method named setup(self) is ignored, so self.num is never set. Accessing self.num causes AttributeError.

❓ framework

advanced

Best practice for sharing setup code in pytest test classes

Which approach is best to share setup code for all test methods in a pytest test class?

A Use a setup_method(self) to initialize instance variables before each test

B Define variables directly inside each test method

C Use __init__(self) method to initialize variables

D Use global variables outside the test class

💡 Hint

pytest calls setup_method automatically before each test method

setup_method(self) is the pytest convention to run setup code before each test method. __init__ is not recommended because pytest creates new instances differently. Defining variables inside each test repeats code. Global variables reduce test isolation.

🧠 Conceptual

expert

Why use test classes in pytest instead of standalone test functions?

What is the main advantage of organizing tests inside classes in pytest?

A To make tests run faster by parallel execution

B To group related tests and share setup/teardown code easily

C To avoid writing assert statements in tests

D To automatically generate test reports without configuration

💡 Hint

Think about code reuse and organization

Test classes help group related tests logically and allow sharing setup and teardown code via methods like setup_method. This improves code organization and reduces duplication. Other options are incorrect because classes do not affect speed, assert statements are always needed, and reports require separate configuration.

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