Reading test data from JSON in Selenium Python - Build an Automation Script

Login test using credentials from JSON file

Preconditions (2)

Step 1: Open the login page URL

Step 2: Read the username and password from 'testdata.json'

Step 3: Enter the username in the email input field with id 'email'

Step 4: Enter the password in the password input field with id 'password'

Step 5: Click the login button with id 'loginBtn'

Step 6: Verify that the URL changes to 'https://example.com/dashboard' after login

✅ Expected Result: User is successfully logged in and redirected to the dashboard page

Automation Requirements - Selenium with Python

Assertions Needed:

Verify the current URL is 'https://example.com/dashboard' after login

Best Practices:

Use explicit waits to wait for elements to be interactable

Use By locators with id for element selection

Read test data from external JSON file

Use try-except blocks to handle exceptions gracefully

Automated Solution

Selenium Python

import json
from selenium import webdriver
from selenium.webdriver.common.by import By
from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.support import expected_conditions as EC
from selenium.common.exceptions import TimeoutException

# Load test data from JSON file
def load_test_data(filepath):
    with open(filepath, 'r', encoding='utf-8') as file:
        return json.load(file)


def test_login_with_json_data():
    data = load_test_data('testdata.json')
    username = data['username']
    password = data['password']

    driver = webdriver.Chrome()
    wait = WebDriverWait(driver, 10)

    try:
        driver.get('https://example.com/login')

        # Wait for email input and enter username
        email_input = wait.until(EC.element_to_be_clickable((By.ID, 'email')))
        email_input.clear()
        email_input.send_keys(username)

        # Wait for password input and enter password
        password_input = wait.until(EC.element_to_be_clickable((By.ID, 'password')))
        password_input.clear()
        password_input.send_keys(password)

        # Wait for login button and click
        login_button = wait.until(EC.element_to_be_clickable((By.ID, 'loginBtn')))
        login_button.click()

        # Wait for URL to change to dashboard
        wait.until(EC.url_to_be('https://example.com/dashboard'))

        assert driver.current_url == 'https://example.com/dashboard', f"Expected URL to be dashboard but got {driver.current_url}"

    except TimeoutException as e:
        assert False, f"Timeout waiting for element or URL change: {e}"

    finally:
        driver.quit()


if __name__ == '__main__':
    test_login_with_json_data()

This script starts by loading the username and password from an external JSON file named testdata.json. This keeps test data separate from code, which is a good practice.

We use Selenium WebDriver to open the login page. Explicit waits ensure the script waits until the email and password fields and the login button are clickable before interacting with them. This avoids errors from trying to use elements too early.

After entering the credentials and clicking login, the script waits until the URL changes to the dashboard URL. Then it asserts that the current URL is exactly the dashboard URL, confirming successful login.

Try-except blocks catch timeout exceptions to fail the test gracefully if elements do not appear in time.

Finally, the browser is closed in the finally block to clean up regardless of test outcome.

Common Mistakes - 4 Pitfalls

Hardcoding test data inside the test script instead of reading from JSON

Using time.sleep() instead of explicit waits

Using incorrect or brittle locators like absolute XPath

Not closing the browser after test execution

Bonus Challenge

Now add data-driven testing with 3 different sets of login credentials read from the JSON file

Show Hint

Practice

1. What is the main benefit of reading test data from a JSON file in Selenium Python tests?

easy

A. It encrypts test data for security.

B. It makes tests run faster by avoiding web interactions.

C. It automatically generates test cases without writing code.

D. It keeps test code clean and makes data easy to update without changing code.

Solution

1. Step 1: Understand test data separation

   Reading test data from JSON separates data from test logic, making code cleaner.

2. Step 2: Recognize flexibility advantage

   Updating test data in JSON does not require changing test scripts, improving flexibility.

3. Final Answer:

   It keeps test code clean and makes data easy to update without changing code. -> Option D

4. Quick Check:

   Data separation = Clean code + Easy updates [OK]

Hint: Separate data from code for easy updates [OK]

Common Mistakes:

• Thinking JSON speeds up test execution
• Believing JSON auto-generates tests
• Confusing data storage with encryption

2. Which Python code snippet correctly reads a JSON file named data.json into a variable test_data?

easy

A. import json
test_data = json.load(open('data.json'))

B. test_data = open('data.json').read()

C. import json
test_data = json.loads('data.json')

D. test_data = json.read('data.json')

Solution

1. Step 1: Identify correct json module usage

   The json.load() function reads JSON from a file object, so open() must be passed to json.load().

2. Step 2: Check syntax correctness

   import json test_data = json.load(open('data.json')) correctly imports json and uses json.load(open('data.json')) to read the file.

3. Final Answer:

   import json\ntest_data = json.load(open('data.json')) -> Option A

4. Quick Check:

   json.load + open(file) = correct JSON read [OK]

Hint: Use json.load() with open() for files [OK]

Common Mistakes:

• Using json.loads() on filename string
• Forgetting to import json module
• Calling non-existent json.read() function

3. Given the JSON file user.json with content:

{"username": "testuser", "password": "pass123"}

and the code:

import json
with open('user.json') as f:
    data = json.load(f)
print(data['username'])

What will be the output?

medium

A. {'username': 'testuser', 'password': 'pass123'}

B. pass123

C. testuser

D. KeyError

Solution

1. Step 1: Load JSON data into dictionary

   The json.load(f) reads the JSON file and converts it into a Python dictionary with keys 'username' and 'password'.

2. Step 2: Access dictionary value by key

   data['username'] accesses the value 'testuser' from the dictionary.

3. Final Answer:

   testuser -> Option C

4. Quick Check:

   data['username'] = 'testuser' [OK]

Hint: Access JSON keys like dictionary keys [OK]

Common Mistakes:

• Printing the whole dictionary instead of key value
• Using wrong key causing KeyError
• Confusing json.load() with json.loads()

4. What is wrong with this code snippet that reads JSON test data?

import json
file = open('data.json')
data = json.load(file)
file.close()
print(data['email'])

Assuming data.json does not contain the key email.

medium

A. The code will raise a KeyError because 'email' key is missing.

B. The print statement syntax is incorrect.

C. The file is not closed properly.

D. json.load() cannot read from open file objects.

Solution

1. Step 1: Understand json.load() behavior

   json.load() correctly reads JSON from an open file object, so no error here.

2. Step 2: Identify missing key issue

   Accessing data['email'] when 'email' key is missing causes a KeyError at runtime.

3. Final Answer:

   The code will raise a KeyError because 'email' key is missing. -> Option A

4. Quick Check:

   Missing key access = KeyError [OK]

Hint: Check keys exist before accessing JSON data [OK]

Common Mistakes:

• Thinking json.load() fails on open files
• Ignoring possible missing keys in JSON
• Assuming file.close() is missing or wrong

5. You want to use JSON test data to fill a login form in Selenium Python. The JSON file login.json contains:

{"username": "user1", "password": "pass1"}

Which code snippet correctly reads the JSON and uses Selenium to fill the form fields with ids user and pass?

hard

A. import json
with open('login.json') as f:
data = json.load(f)
driver.find_element_by_name('user').send_keys(data['username'])
driver.find_element_by_name('pass').send_keys(data['password'])

B. import json
with open('login.json') as f:
data = json.load(f)
driver.find_element('id', 'user').send_keys(data['username'])
driver.find_element('id', 'pass').send_keys(data['password'])

C. import json
with open('login.json') as f:
data = json.loads(f)
driver.find_element_by_id('user').send_keys(data['username'])
driver.find_element_by_id('pass').send_keys(data['password'])

D. import json
with open('login.json') as f:
data = json.load(f)
driver.find_element('name', 'user').send_keys(data['username'])
driver.find_element('name', 'pass').send_keys(data['password'])

Solution

1. Step 1: Correctly read JSON file

   json.load(f) reads JSON from file object correctly; json.loads() expects a string, so import json with open('login.json') as f: data = json.loads(f) driver.find_element_by_id('user').send_keys(data['username']) driver.find_element_by_id('pass').send_keys(data['password']) is wrong.

2. Step 2: Use correct Selenium locator method

   driver.find_element('id', 'user') is the modern syntax to find element by id; find_element_by_id() is deprecated.

3. Step 3: Match locators with element ids

   The form fields have ids 'user' and 'pass', so locating by id is correct, not by name.

4. Final Answer:

   import json with open('login.json') as f: data = json.load(f) driver.find_element('id', 'user').send_keys(data['username']) driver.find_element('id', 'pass').send_keys(data['password']) -> Option B

5. Quick Check:

   json.load + find_element('id', ...) = correct usage [OK]

Hint: Use json.load() and find_element('id', ...) for form filling [OK]

Common Mistakes:

• Using json.loads() on file object
• Using deprecated find_element_by_id()
• Using wrong locator type (name instead of id)