Given-When-Then pattern in PyTest - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this pytest Given-When-Then test?

Consider this pytest test using the Given-When-Then pattern. What will be the test result?

PyTest

import pytest

def add(a, b):
    return a + b

def test_addition():
    # Given two numbers
    x = 3
    y = 4

    # When they are added
    result = add(x, y)

    # Then the result should be 7
    assert result == 7

A Test passes successfully

B Test fails with AssertionError

C Test raises a NameError

D Test raises a TypeError

💡 Hint

Check the add function and the assertion carefully.

The add function correctly sums 3 and 4 to 7. The assertion checks if result == 7, which is true, so the test passes.

❓ assertion

intermediate

Which assertion correctly follows the Then step in Given-When-Then?

You want to check that a function returns a list with exactly 3 items. Which assertion fits the Then step best?

A assert result is not None

B assert len(result) == 3

C assert result[0] == 3

D assert type(result) == dict

💡 Hint

Focus on checking the number of items in the list.

The Then step verifies the expected outcome. Checking length equals 3 confirms the list size is correct.

🔧 Debug

advanced

Why does this Given-When-Then test fail?

This pytest test using Given-When-Then fails. What is the cause?

PyTest

def multiply(a, b):
    return a * b

def test_multiply():
    # Given two numbers
    x = 2
    y = 5

    # When they are multiplied
    result = multiply(x, y)

    # Then the result should be 15
    assert result == 15

A The assertion syntax is invalid

B The multiply function has a syntax error

C The variables x and y are not defined

D The expected result in Then step is incorrect

💡 Hint

Calculate 2 times 5 and compare with the expected result.

2 multiplied by 5 equals 10, but the test expects 15, so the assertion fails.

🧠 Conceptual

advanced

What is the main purpose of the Given-When-Then pattern in testing?

Choose the best description of the Given-When-Then pattern's purpose.

A To write tests that run faster by skipping setup steps

B To replace all assertions with print statements

C To structure tests clearly by separating setup, action, and verification

D To avoid writing any code in the test functions

💡 Hint

Think about how tests are organized for clarity.

Given-When-Then helps organize tests into setup (Given), action (When), and check (Then) for readability and maintainability.

❓ framework

expert

Which pytest fixture usage best fits the Given step in Given-When-Then?

You want to prepare test data before running the test action. Which fixture usage fits the Given step best?

A

@pytest.fixture
def setup_data():
    return {'user': 'alice', 'age': 30}

# In test:
# def test_user(setup_data):
#     ...

B

@pytest.mark.parametrize('input', [1, 2, 3])
def test_numbers(input):
    ...

C

def test_action():
    result = do_something()
    assert result is True

D

@pytest.fixture
def teardown_data():
    print('Cleaning up')

💡 Hint

Given step prepares data or state before the action.

Fixture setup_data prepares test data before the test runs, matching the Given step role.

Practice

1. What is the main purpose of the Given-When-Then pattern in pytest tests?

easy

A. To write tests only for user interface elements

B. To organize tests into setup, action, and verification steps

C. To speed up test execution by skipping setup

D. To avoid using assertions in tests

Solution

1. Step 1: Understand the pattern roles

   Given-When-Then divides a test into three parts: Given (setup), When (action), Then (check).

2. Step 2: Match purpose with options

   Only To organize tests into setup, action, and verification steps correctly describes this organization purpose.

3. Final Answer:

   To organize tests into setup, action, and verification steps -> Option B

4. Quick Check:

   Given-When-Then = organize test steps [OK]

Hint: Remember: Given=setup, When=action, Then=check [OK]

Common Mistakes:

• Thinking it only applies to UI tests
• Believing it skips setup steps
• Assuming no assertions are used

2. Which of the following is the correct way to write a Given-When-Then style pytest test function?

easy

A. def test_example():
# Given
x = 5
# When
y = x + 3
# Then
assert y == 8

B. def test_example():
x = 5
y = x + 3
assert y == 8
# Given-When-Then comments missing

C. def test_example():
assert 5 + 3 == 8
# Given-When-Then not used

D. def test_example():
# When
x = 5
# Given
y = x + 3
# Then
assert y == 8

Solution

1. Step 1: Check comment order and code logic

   def test_example(): # Given x = 5 # When y = x + 3 # Then assert y == 8 correctly uses Given-When-Then comments in order with proper setup, action, and assertion.

2. Step 2: Identify incorrect patterns

   The other options either lack Given-When-Then comments or have them in the wrong order (e.g., When before Given).

3. Final Answer:

   def test_example():\n # Given\n x = 5\n # When\n y = x + 3\n # Then\n assert y == 8 -> Option A

4. Quick Check:

   Correct comment order = def test_example(): # Given x = 5 # When y = x + 3 # Then assert y == 8 [OK]

Hint: Follow comment order: Given, When, Then [OK]

Common Mistakes:

• Mixing the order of Given and When comments
• Skipping comments entirely
• Placing assertions outside Then step

3. Given the following pytest test using Given-When-Then pattern, what will be the test result?

def test_sum():
    # Given
    numbers = [1, 2, 3]
    # When
    total = sum(numbers)
    # Then
    assert total == 6

medium

A. Test will fail because assertion is wrong

B. Test will fail because sum is calculated incorrectly

C. Test will error due to missing import

D. Test will pass because sum of [1, 2, 3] is 6

Solution

1. Step 1: Calculate sum of list

   The sum of [1, 2, 3] is 1+2+3 = 6.

2. Step 2: Check assertion correctness

   The assertion checks total == 6, which is true, so test passes.

3. Final Answer:

   Test will pass because sum of [1, 2, 3] is 6 -> Option D

4. Quick Check:

   sum([1,2,3]) = 6 [OK]

Hint: Calculate sum and compare with assertion value [OK]

Common Mistakes:

• Assuming sum returns a list instead of number
• Thinking assertion expects a different value
• Confusing test error with failure

4. Identify the error in this Given-When-Then pytest test:

def test_multiply():
    # Given
    x = 4
    y = 5
    # When
    result = x * y
    # Then
    assert result = 20

medium

A. Syntax error in assertion statement

B. Wrong variable names used

C. Missing setup in Given step

D. No assertion in Then step

Solution

1. Step 1: Check assertion syntax

   The assertion uses single '=' which is assignment, not comparison. It should be '==' for comparison.

2. Step 2: Confirm other parts are correct

   Variables and steps are correct; only assertion syntax is wrong.

3. Final Answer:

   Syntax error in assertion statement -> Option A

4. Quick Check:

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

Hint: Use '==' for assert comparisons, not '=' [OK]

Common Mistakes:

• Using '=' instead of '==' in assert
• Confusing assignment with comparison
• Ignoring syntax errors in assertions

5. You want to test a function that filters out falsy values (like 0, '', None) from a list using Given-When-Then pattern in pytest. Which test code correctly applies this pattern and checks the result?

hard

A. def test_filter_falsy():
# Given
data = [0, 1, '', 'hello', None, True]
# Then
assert filtered == [1, 'hello', True]
# When
filtered = [x for x in data if x]

B. def test_filter_falsy():
data = [0, 1, '', 'hello', None, True]
filtered = [x for x in data if x]
assert filtered == [1, 'hello', True]

C. def test_filter_falsy():
# Given
data = [0, 1, '', 'hello', None, True]
# When
filtered = [x for x in data if x]
# Then
assert filtered == [1, 'hello', True]

D. def test_filter_falsy():
# Given
data = [0, 1, '', 'hello', None, True]
# When
filtered = filter(lambda x: x, data)
# Then
assert list(filtered) == [0, 1, '', 'hello', None, True]

Solution

1. Step 1: Verify Given-When-Then structure

   def test_filter_falsy(): # Given data = [0, 1, '', 'hello', None, True] # When filtered = [x for x in data if x] # Then assert filtered == [1, 'hello', True] correctly uses Given for data setup, When for filtering action, Then for assertion check.

2. Step 2: Check correctness of filtering and assertion

   Filtering removes falsy values; expected list matches filtered result. Other options miss comments or have wrong assertion.

3. Final Answer:

   def test_filter_falsy():\n # Given\n data = [0, 1, '', 'hello', None, True]\n # When\n filtered = [x for x in data if x]\n # Then\n assert filtered == [1, 'hello', True] -> Option C

4. Quick Check:

   Given-When-Then + correct filter = def test_filter_falsy(): # Given data = [0, 1, '', 'hello', None, True] # When filtered = [x for x in data if x] # Then assert filtered == [1, 'hello', True] [OK]

Hint: Keep steps clear: setup, action, then check [OK]

Common Mistakes:

• Skipping Given-When-Then comments
• Asserting wrong filtered list
• Using filter object without converting to list