@pytest.mark.parametrize decorator - Framework Patterns

Framework Mode - @pytest.mark.parametrize decorator

Folder Structure

tests/
├── test_example.py       # Test files using @pytest.mark.parametrize
├── conftest.py           # Fixtures and hooks
utilities/
├── helpers.py            # Helper functions
config/
├── config.yaml           # Environment and test settings
reports/
├── latest_report.html    # Test run reports

Test Framework Layers

• Test Layer: Contains test files like test_example.py where @pytest.mark.parametrize is used to run the same test with different inputs.
• Fixtures Layer: conftest.py holds setup and teardown code shared across tests.
• Utilities Layer: Helper functions and reusable code to support tests.
• Configuration Layer: Stores environment variables, credentials, and test parameters in config.yaml or similar files.
• Reporting Layer: Generates test reports after execution, stored in reports/.

Configuration Patterns

• Use config.yaml or config.json to store environment URLs, browser options, and credentials.
• Load configuration in conftest.py using fixtures to provide data to tests.
• Use @pytest.mark.parametrize to pass multiple sets of test data directly in test functions or load from external files.
• Keep sensitive data out of code by using environment variables or encrypted files.

Test Reporting and CI/CD Integration

• Use pytest plugins like pytest-html or pytest-json-report to generate readable reports.
• Reports are saved in reports/ folder for easy access.
• Integrate tests into CI/CD pipelines (GitHub Actions, Jenkins) to run tests automatically on code changes.
• Failing tests with @pytest.mark.parametrize show which input data caused failure for quick debugging.

Best Practices

1. Use @pytest.mark.parametrize to avoid repeating similar test code for different inputs.
2. Keep test data simple and readable; use descriptive parameter names.
3. Combine @pytest.mark.parametrize with fixtures for flexible and maintainable tests.
4. Organize test data in separate files if it grows large, and load it dynamically.
5. Write clear assertions so failures show exactly what input caused the problem.

Self Check

Where in this folder structure would you add a new test file that uses @pytest.mark.parametrize to test login functionality with multiple username and password combinations?

Key Result

Use @pytest.mark.parametrize in test files under tests/ to run the same test with multiple input sets efficiently.

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