Test functions in PyTest - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple pytest test function

What is the test result when running this pytest test function?

PyTest

def test_sum():
    assert 2 + 3 == 5

A SyntaxError due to missing colon

B Test fails with AssertionError

C Test passes with no errors

D TypeError because of wrong assertion

💡 Hint

Check if the assertion condition is true.

The assertion 2 + 3 == 5 is true, so the test passes without errors.

❓ assertion

intermediate

Identify the failing assertion in pytest

Which assertion will cause the pytest test to fail?

PyTest

def test_values():
    assert 10 > 5
    assert 'a' == 'b'
    assert [1, 2] == [1, 2]

A assert 'a' == 'b'

B assert [1, 2] == [1, 2]

C assert 10 > 5

D All assertions pass

💡 Hint

Check which condition is false.

The assertion 'a' == 'b' is false, so pytest will fail at this line.

🔧 Debug

advanced

Find the error in this pytest test function

What error will pytest report when running this test function?

PyTest

def test_division():
    result = 10 / 0
    assert result == 0

A ZeroDivisionError at runtime

B Test passes successfully

C SyntaxError due to missing colon

D AssertionError because result is not 0

💡 Hint

Consider what happens when dividing by zero in Python.

Dividing by zero raises a ZeroDivisionError before the assertion runs.

❓ framework

advanced

pytest test discovery rules

Which function name will pytest automatically discover as a test?

A def example_test():

B def test_example():

C def check_test():

D def example():

💡 Hint

pytest looks for functions starting with a specific prefix.

pytest discovers functions starting with test_ as tests.

🧠 Conceptual

expert

Effect of multiple assertions in one pytest test function

What happens when multiple assertions exist in one pytest test function and the first assertion fails?

A pytest retries the test automatically on failure

B All assertions run; all failures are reported together

C Test passes if any assertion passes

D Test stops at first failed assertion; later assertions are not checked

💡 Hint

Think about how Python handles exceptions during test execution.

When an assertion fails, it raises an exception stopping the test function immediately.

Practice

1. What is the main purpose of a test function in pytest?

easy

A. To create user interfaces

B. To run the program faster

C. To check if the code works as expected

D. To store data permanently

Solution

1. Step 1: Understand the role of test functions

   Test functions are written to verify that the code behaves correctly.

2. Step 2: Identify the main goal

   The main goal is to check if the code works as expected, catching bugs early.

3. Final Answer:

   To check if the code works as expected -> Option C

4. Quick Check:

   Test functions = Verify code correctness [OK]

Hint: Test functions verify code behavior, not speed or UI [OK]

Common Mistakes:

• Thinking test functions improve program speed
• Confusing test functions with UI code
• Assuming test functions store data

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

easy

A. check_function()

B. TestFunction()

C. function_test()

D. test_function()

Solution

1. Step 1: Recall pytest naming rules

   Pytest requires test functions to start with 'test_' to be recognized automatically.

2. Step 2: Identify the correct naming

   Only 'test_function()' starts with 'test_', so it is correct.

3. Final Answer:

   test_function() -> Option D

4. Quick Check:

   Test function names start with 'test_' [OK]

Hint: Test functions must start with 'test_' prefix [OK]

Common Mistakes:

• Using names without 'test_' prefix
• Capitalizing function names incorrectly
• Placing 'test' at the end of the name

3. What will be the result of running this pytest test function?

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

medium

A. Test passes successfully

B. Test fails with AssertionError

C. SyntaxError occurs

D. Test is skipped automatically

Solution

1. Step 1: Analyze the test code

   The function calculates 2 + 3 and stores in 'result'.

2. Step 2: Check the assertion

   The assertion checks if 'result' equals 5, which is true.

3. Final Answer:

   Test passes successfully -> Option A

4. Quick Check:

   2 + 3 == 5 means test passes [OK]

Hint: If assert condition is true, test passes [OK]

Common Mistakes:

• Assuming assertion fails when it is true
• Confusing syntax errors with assertion errors
• Thinking tests skip without skip decorators

4. Identify the error in this pytest test function:

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

medium

A. Incorrect assert syntax using '=' instead of '=='

B. Function name does not start with 'test_'

C. Multiplication operator '*' is invalid

D. Missing return statement in test function

Solution

1. Step 1: Check the assert statement syntax

   The assert statement uses '=' which is assignment, not comparison.

2. Step 2: Identify correct syntax

   Assert requires '==' to compare values, so '=' causes a syntax error.

3. Final Answer:

   Incorrect assert syntax using '=' instead of '==' -> Option A

4. Quick Check:

   Use '==' in assert, not '=' [OK]

Hint: Assert needs '==' for comparison, '=' causes error [OK]

Common Mistakes:

• Using '=' instead of '==' in assert
• Ignoring function naming rules
• Thinking return is needed in test functions

5. You want to test a function that returns the maximum number from a list. Which pytest test function below correctly tests this behavior including an edge case for an empty list?

def max_number(numbers):
    return max(numbers)

# Choose the correct test function:

hard

A. def test_max_number():
assert max_number([1, 3, 2]) == 3
assert max_number([]) == None

B. def test_max_number():
assert max_number([1, 3, 2]) == 3
import pytest
with pytest.raises(ValueError):
max_number([])

C. def test_max_number():
assert max_number([1, 3, 2]) == 2
assert max_number([0]) == 0

D. def test_max_number():
assert max_number([1, 3, 2]) == 3
assert max_number([1, 3, 2]) == 1

Solution

1. Step 1: Understand max() behavior on empty list

   Calling max([]) raises ValueError, so test must expect this error.

2. Step 2: Check which test handles empty list correctly

   def test_max_number(): assert max_number([1, 3, 2]) == 3 import pytest with pytest.raises(ValueError): max_number([]) uses pytest.raises to check for ValueError, correctly testing the edge case.

3. Final Answer:

   Test function that asserts max and expects ValueError on empty list -> Option B

4. Quick Check:

   Use pytest.raises for exceptions in tests [OK]

Hint: Use pytest.raises to test expected errors [OK]

Common Mistakes:

• Assuming max([]) returns None instead of error
• Wrong expected max value in assertions
• Testing same input with conflicting expected outputs