Parameterized tests in Selenium Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of parameterized Selenium test with multiple inputs

Consider this parameterized Selenium test using pytest. What will be the output when running this test suite?

Selenium Python

import pytest
from selenium.webdriver.common.by import By

@pytest.mark.parametrize('search_term', ['apple', 'banana'])
def test_search(browser, search_term):
    browser.get('https://example.com')
    search_box = browser.find_element(By.NAME, 'q')
    search_box.send_keys(search_term)
    search_box.submit()
    assert search_term in browser.title

A Both tests pass if page title contains 'apple' and 'banana' respectively

B Tests run but assertion always fails due to wrong locator

C Both tests fail because 'browser' fixture is not defined

D Only the first test runs because parameterization is incorrect

💡 Hint

Think about what is missing for the test to run properly with Selenium.

The test uses a 'browser' argument but does not define a fixture or setup for it. Without a browser fixture, pytest cannot provide the 'browser' object, so the tests will fail to run.

❓ assertion

intermediate

Correct assertion in parameterized test for form validation

You have a parameterized test that submits a form with different inputs. Which assertion correctly verifies that the error message appears when input is invalid?

Selenium Python

import pytest
from selenium.webdriver.common.by import By

@pytest.mark.parametrize('input_value, expect_error', [('', True), ('valid', False)])
def test_form_validation(browser, input_value, expect_error):
    browser.get('https://example.com/form')
    input_field = browser.find_element(By.ID, 'input')
    input_field.clear()
    input_field.send_keys(input_value)
    submit_button = browser.find_element(By.ID, 'submit')
    submit_button.click()
    error_elements = browser.find_elements(By.CLASS_NAME, 'error')
    # Which assertion is correct?

A assert (len(error_elements) > 0) == expect_error

B assert error_elements.text == expect_error

C assert error_elements.is_displayed() == expect_error

D assert error_elements.exists() == expect_error

💡 Hint

Remember that find_elements returns a list, not a single element.

find_elements returns a list of matching elements. To check if errors appear, verify if the list length is greater than zero and compare it to the expected error presence.

❓ locator

advanced

Best locator strategy for parameterized test with dynamic IDs

In a parameterized test, you need to locate a button whose ID changes dynamically but always starts with 'btn_'. Which locator is best to use?

A By.CLASS_NAME, 'btn_'

B By.ID, 'btn_' + dynamic_part

C By.XPATH, '//button[contains(@id, "btn_")]'

D By.CSS_SELECTOR, 'button[id^="btn_"]'

💡 Hint

Look for a locator that matches the start of the ID attribute.

CSS selector with ^= matches elements whose attribute starts with a given string. This is efficient and reliable for dynamic IDs starting with 'btn_'.

🔧 Debug

advanced

Debugging flaky parameterized Selenium test

A parameterized Selenium test intermittently fails with 'ElementNotInteractableException' on clicking a button. What is the most likely cause?

Selenium Python

import pytest
from selenium.webdriver.common.by import By

@pytest.mark.parametrize('page', ['home', 'about'])
def test_click_button(browser, page):
    browser.get(f'https://example.com/{page}')
    button = browser.find_element(By.ID, 'start')
    button.click()
    assert 'Started' in browser.page_source

A The parameterization syntax is invalid causing test failure

B The button is not visible or ready when click is attempted

C The locator ID 'start' is incorrect on some pages

D The assertion is wrong and causes false failures

💡 Hint

Consider timing and element readiness in Selenium tests.

ElementNotInteractableException usually means the element is present but not interactable yet, often due to page loading or animations. Adding waits can fix this.

❓ framework

expert

Implementing parameterized tests with pytest and Selenium for multiple browsers

You want to run the same parameterized test on Chrome and Firefox browsers using pytest and Selenium. Which pytest fixture setup correctly supports this?

A Use @pytest.mark.parametrize('browser_name', ['chrome', 'firefox']) and a fixture that initializes WebDriver based on browser_name

B Create separate test functions for each browser without parameterization

C Use a global variable to switch browsers inside the test

D Use Selenium Grid without any pytest parameterization

💡 Hint

Think about combining pytest parameterization with fixtures for browser setup.

Parametrizing the browser name and using a fixture to initialize the correct WebDriver allows running the same test on multiple browsers cleanly.

Practice

1. What is the main benefit of using @pytest.mark.parametrize in Selenium Python tests?

easy

A. It allows running the same test with multiple sets of data easily.

B. It speeds up the browser loading time.

C. It automatically finds locators on the page.

D. It generates test reports without extra code.

Solution

1. Step 1: Understand the purpose of parameterized tests

   Parameterized tests run the same test logic multiple times with different input data sets.

2. Step 2: Identify what @pytest.mark.parametrize does

   This decorator allows easy setup of multiple data inputs for one test function, reducing repeated code.

3. Final Answer:

   It allows running the same test with multiple sets of data easily. -> Option A

4. Quick Check:

   Parameterized tests = multiple data sets [OK]

Hint: Think: same test, many inputs, less code [OK]

Common Mistakes:

• Confusing parameterization with browser speed optimization
• Thinking it auto-finds locators
• Assuming it auto-generates reports

2. Which of the following is the correct syntax to parameterize a test function with two parameters username and password using pytest?

easy

A. @pytest.mark.param('username', 'password', [('user1', 'pass1'), ('user2', 'pass2')])

B. @pytest.parametrize(['username', 'password'], [('user1', 'pass1'), ('user2', 'pass2')])

C. @pytest.mark.parametrize(('username', 'password'), ['user1', 'pass1', 'user2', 'pass2'])

D. @pytest.mark.parametrize('username, password', [('user1', 'pass1'), ('user2', 'pass2')])

Solution

1. Step 1: Recall pytest parameterize syntax

   The correct syntax uses @pytest.mark.parametrize with a string of comma-separated parameter names and a list of tuples for values.

2. Step 2: Compare options

   @pytest.mark.parametrize('username, password', [('user1', 'pass1'), ('user2', 'pass2')]) matches the correct syntax exactly. Others have wrong decorator names or wrong argument formats.

3. Final Answer:

   @pytest.mark.parametrize('username, password', [('user1', 'pass1'), ('user2', 'pass2')]) -> Option D

4. Quick Check:

   Correct decorator and tuple list = @pytest.mark.parametrize('username, password', [('user1', 'pass1'), ('user2', 'pass2')]) [OK]

Hint: Remember: mark.parametrize with string params and list of tuples [OK]

Common Mistakes:

• Misspelling 'parametrize' as 'parametrize' or 'param'
• Using list instead of tuple for parameter values
• Passing parameters as list instead of string

3. What will be the output when running this parameterized test snippet?

import pytest

@pytest.mark.parametrize('num, expected', [(1, 2), (2, 3), (3, 4)])
def test_increment(num, expected):
    assert num + 1 == expected

medium

A. Syntax error due to wrong decorator usage.

B. All tests fail due to assertion errors.

C. All tests pass successfully.

D. Only the first test passes, others fail.

Solution

1. Step 1: Analyze the test logic and parameters

   Each tuple provides num and expected. The test asserts num + 1 == expected. For (1,2), 1+1=2; for (2,3), 2+1=3; for (3,4), 3+1=4.

2. Step 2: Check if assertions hold for all cases

   All assertions are true, so all tests pass.

3. Final Answer:

   All tests pass successfully. -> Option C

4. Quick Check:

   num + 1 equals expected for all [OK]

Hint: Check each input-output pair matches assertion [OK]

Common Mistakes:

• Assuming some tests fail without checking values
• Confusing parameter order
• Thinking decorator syntax is wrong

4. Identify the error in this parameterized test code:

import pytest

@pytest.mark.parametrize('input, expected')
def test_double(input, expected):
    assert input * 2 == expected

@pytest.mark.parametrize('input, expected', [(2, 4), (3, 6)])

medium

A. Wrong assertion operator used.

B. Missing data list for parameterize decorator on test_double.

C. Parameters names should be a list, not a string.

D. Test function name is invalid.

Solution

1. Step 1: Check the decorator usage on test_double

   The decorator @pytest.mark.parametrize('input, expected') is missing the second argument: the list of data tuples.

2. Step 2: Verify other parts

   Assertion and function name are correct. Parameter names as string is valid syntax.

3. Final Answer:

   Missing data list for parameterize decorator on test_double. -> Option B

4. Quick Check:

   Decorator needs data list argument [OK]

Hint: Always provide data list with parametrize decorator [OK]

Common Mistakes:

• Forgetting the data list argument
• Using list instead of string for parameter names (which is allowed but less common)
• Misreading assertion syntax

5. You want to test a login form with multiple username and password pairs using Selenium and pytest parameterization. Which approach correctly combines parameterized tests with Selenium WebDriver to test login functionality?

hard

A. Use @pytest.mark.parametrize to pass username and password, then inside the test open the browser, fill fields, submit, and assert login success.

B. Write separate test functions for each username and password pair without parameterization.

C. Use parameterization only for URLs, not for form inputs like username and password.

D. Use @pytest.mark.parametrize but do not open the browser inside the test function.

Solution

1. Step 1: Understand parameterized test purpose in Selenium context

   Parameterized tests allow running the same test logic with different input data, such as username and password pairs.

2. Step 2: Combine parameterization with Selenium actions

   Inside the test function, open the browser, fill the login form with parameters, submit, and check results. This is the correct approach.

3. Final Answer:

   Use @pytest.mark.parametrize to pass username and password, then inside the test open the browser, fill fields, submit, and assert login success. -> Option A

4. Quick Check:

   Parameterize inputs + Selenium actions inside test [OK]

Hint: Parameterize inputs, then automate browser steps inside test [OK]

Common Mistakes:

• Writing separate tests instead of parameterizing
• Not opening browser inside test function
• Limiting parameterization to URLs only