@pytest.mark.parametrize decorator - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to parametrize the test function with two values for x.

PyTest

import pytest

@pytest.mark.parametrize('x', [[1]])
def test_example(x):
    assert x > 0

Drag options to blanks, or click blank then click option'

A1 2

B1, 2

C(1, 2)

D'1, 2'

Attempts:

3 left

💡 Hint

Common Mistakes

Using space instead of comma to separate values

Passing a tuple instead of a list

Passing a string instead of a list

The @pytest.mark.parametrize decorator expects a list of values. Using 1, 2 inside the list creates two values to test.

2fill in blank

medium

Complete the code to parametrize the test function with two parameters: x and y.

PyTest

import pytest

@pytest.mark.parametrize([1], [(1, 2), (3, 4)])
def test_sum(x, y):
    assert x + y > 0

Drag options to blanks, or click blank then click option'

A'(x, y)'

B['x', 'y']

C'x, y'

D('x', 'y')

Attempts:

3 left

💡 Hint

Common Mistakes

Passing parameter names as a list instead of a string

Using parentheses instead of quotes

Including spaces inside the string incorrectly

The parameter names must be passed as a single string with names separated by commas inside @pytest.mark.parametrize.

3fill in blank

hard

Fix the error in the parametrize decorator to correctly test multiple sets of inputs.

PyTest

import pytest

@pytest.mark.parametrize('x, y', [1])
def test_multiply(x, y):
    assert x * y >= 0

Drag options to blanks, or click blank then click option'

A[(1, 2), (3,)]

B[1, 2, 3, 4]

C[(1, 2), 3, 4]

D[(1, 2), (3, 4)]

Attempts:

3 left

💡 Hint

Common Mistakes

Passing a flat list instead of list of tuples

Tuples with missing elements

Mixing tuples and single values

The values must be a list of tuples, each tuple matching the parameters. Option D correctly provides two tuples.

4fill in blank

hard

Fill both blanks to parametrize the test with three sets of inputs and check the sum.

PyTest

import pytest

@pytest.mark.parametrize([1], [2])
def test_sum(x, y):
    assert x + y == 3

Drag options to blanks, or click blank then click option'

A'x, y'

B[(1, 2), (2, 1), (0, 3)]

C[(1, 2), (2, 2), (0, 3)]

D'x,y'

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect parameter string format

Using tuples with wrong sums

Using lists instead of tuples for values

The parameter names must be a string with comma-separated names (option A). The values must be a list of tuples matching the parameters (option B).

5fill in blank

hard

Fill all three blanks to parametrize the test with parameters a, b and expected, and check the multiplication result.

PyTest

import pytest

@pytest.mark.parametrize([1], [2])
def test_multiply(a, b, expected):
    assert a * b == [3]

Drag options to blanks, or click blank then click option'

A'a, b, expected'

B[(2, 3, 6), (4, 5, 20), (1, 0, 0)]

Cexpected

D'a, b'

Attempts:

3 left

💡 Hint

Common Mistakes

Mismatching parameter names and values

Using wrong variable in assertion

Incorrect tuple lengths in values

The parameter names are a string with three names (option A). The values are a list of tuples with three elements each (option B). The assertion compares the product to the expected value (option C).

Practice

1. What is the main purpose of the @pytest.mark.parametrize decorator in pytest?

easy

A. To skip a test function during test execution

B. To run the same test function multiple times with different input values

C. To mark a test as expected to fail

D. To group multiple test functions into a test suite

Solution

1. Step 1: Understand the decorator's role

   @pytest.mark.parametrize allows running one test function multiple times with different inputs.

2. Step 2: Compare options with this role

   Only To run the same test function multiple times with different input values describes running the same test with different inputs, matching the decorator's purpose.

3. Final Answer:

   To run the same test function multiple times with different input values -> Option B

4. Quick Check:

   Parametrize = multiple inputs [OK]

Hint: Parametrize means run test many times with different data [OK]

Common Mistakes:

• Confusing parametrize with skipping tests
• Thinking it groups tests instead of repeating one
• Mixing it up with marking expected failures

2. Which of the following is the correct syntax to use @pytest.mark.parametrize for testing a function with inputs 1 and 2?

easy

A. @pytest.mark.parametrized('input', [1, 2])

B. @pytest.parametrize('input', (1, 2))

C. @pytest.mark.parametrize(input, [1, 2])

D. @pytest.mark.parametrize('input', [1, 2])

Solution

1. Step 1: Check correct decorator name and syntax

   The correct decorator is @pytest.mark.parametrize with parameters as strings and list of values.

2. Step 2: Validate each option

   @pytest.mark.parametrize('input', [1, 2]) uses correct spelling, quotes around parameter name, and list syntax. Others have syntax errors or wrong names.

3. Final Answer:

   @pytest.mark.parametrize('input', [1, 2]) -> Option D

4. Quick Check:

   Correct spelling and syntax = @pytest.mark.parametrize('input', [1, 2]) [OK]

Hint: Decorator name is mark.parametrize with string param name [OK]

Common Mistakes:

• Misspelling 'parametrize' as 'parametrized'
• Forgetting quotes around parameter name
• Using wrong brackets or missing @ symbol

3. What will be the output when running this pytest code?

import pytest

@pytest.mark.parametrize('x,y', [(1,2), (3,4)])
def test_sum(x, y):
    assert x + y == 3

medium

A. First test passes, second test fails

B. Both tests fail

C. Both tests pass

D. Syntax error during test collection

Solution

1. Step 1: Analyze test cases and assertion

   Test runs twice: (1,2) and (3,4). Assertion checks if sum equals 3.

2. Step 2: Evaluate each case

   1+2=3 passes; 3+4=7 fails assertion.

3. Final Answer:

   First test passes, second test fails -> Option A

4. Quick Check:

   Sum check true only for (1,2) [OK]

Hint: Check each input pair sum against assertion [OK]

Common Mistakes:

• Assuming all tests pass without checking values
• Confusing tuple unpacking in parametrize
• Ignoring assertion logic

4. Identify the error in this pytest code using @pytest.mark.parametrize:

@pytest.mark.parametrize('num', [1, 2, 3])
def test_even():
    assert num % 2 == 0

medium

A. Wrong decorator name

B. List of values should be a tuple

C. Missing parameter in test function definition

D. Assertion logic is incorrect

Solution

1. Step 1: Check function parameters

   Test function must accept the parameter named in parametrize ('num'), but test_even() has no parameters.

2. Step 2: Confirm other parts

   Decorator name and list syntax are correct; assertion logic is valid for even check.

3. Final Answer:

   Missing parameter in test function definition -> Option C

4. Quick Check:

   Function must accept parametrize variables [OK]

Hint: Test function needs parameters matching parametrize names [OK]

Common Mistakes:

• Forgetting to add parameters to test function
• Thinking list must be tuple
• Confusing assertion logic with syntax error

5. You want to test a function is_valid_age(age) that returns True if age is between 18 and 65 inclusive. Which @pytest.mark.parametrize usage correctly tests ages 17, 18, 30, 65, and 70 with expected results?

hard

A. @pytest.mark.parametrize(['age', 'expected'], [(17, False), (18, True), (30, True), (65, True), (70, False)])

B. @pytest.mark.parametrize('age', [17, 18, 30, 65, 70], 'expected', [False, True, True, True, False])

C. @pytest.mark.parametrize('age,expected', {17: False, 18: True, 30: True, 65: True, 70: False})

D. @pytest.mark.parametrize(age,expected, [(17, False), (18, True), (30, True), (65, True), (70, False)])

Solution

1. Step 1: Understand parametrize syntax for multiple parameters

   When passing multiple parameters, use a string with comma-separated names or a list of strings as first argument, and a list of tuples as second.

2. Step 2: Evaluate each option

   A: @pytest.mark.parametrize(age,expected, [(17, False), (18, True), (30, True), (65, True), (70, False)]) misses quotes around parameter names, causing error. B has wrong syntax with multiple arguments. C uses a dict, which is invalid. D: @pytest.mark.parametrize(['age', 'expected'], [(17, False), (18, True), (30, True), (65, True), (70, False)]) uses list of strings correctly.

3. Step 3: Choose best practice

   @pytest.mark.parametrize(['age', 'expected'], [(17, False), (18, True), (30, True), (65, True), (70, False)]) is correct and clear syntax for multiple parameters.

4. Final Answer:

   @pytest.mark.parametrize(['age', 'expected'], [(17, False), (18, True), (30, True), (65, True), (70, False)]) -> Option A

5. Quick Check:

   List of param names + list of tuples = @pytest.mark.parametrize(['age', 'expected'], [(17, False), (18, True), (30, True), (65, True), (70, False)]) [OK]

Hint: Use list of param names and list of tuples for multiple inputs [OK]

Common Mistakes:

• Passing multiple parameter lists separately
• Using dict instead of list of tuples
• Confusing string vs list for parameter names