Reading test data from CSV in Selenium Python - Test Execution Trace

Test Overview

This test reads login credentials from a CSV file and verifies successful login on a web page using Selenium.

Test Code - Selenium

Selenium Python

import csv
import unittest
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

class TestLoginWithCSV(unittest.TestCase):
    def setUp(self):
        self.driver = webdriver.Chrome()
        self.driver.get('https://example.com/login')

    def test_login_from_csv(self):
        with open('testdata.csv', newline='') as csvfile:
            reader = csv.DictReader(csvfile)
            for row in reader:
                username = row['username']
                password = row['password']

                username_field = WebDriverWait(self.driver, 10).until(
                    EC.presence_of_element_located((By.ID, 'username'))
                )
                username_field.clear()
                username_field.send_keys(username)

                password_field = self.driver.find_element(By.ID, 'password')
                password_field.clear()
                password_field.send_keys(password)

                login_button = self.driver.find_element(By.ID, 'login-btn')
                login_button.click()

                welcome_message = WebDriverWait(self.driver, 10).until(
                    EC.presence_of_element_located((By.ID, 'welcome-msg'))
                )
                self.assertIn('Welcome', welcome_message.text)

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

    def tearDown(self):
        self.driver.quit()

if __name__ == '__main__':
    unittest.main()

Execution Trace - 9 Steps

Step	Action	System State	Assertion	Result
1	Test starts and Chrome browser opens	Browser opened at https://example.com/login page	—	PASS
2	Reads first row from CSV file with username and password	CSV file opened and first credentials loaded	—	PASS
3	Finds username input field by ID 'username' and enters username	Username field visible and filled with username	—	PASS
4	Finds password input field by ID 'password' and enters password	Password field visible and filled with password	—	PASS
5	Finds login button by ID 'login-btn' and clicks it	Login button clicked, page loading	—	PASS
6	Waits for welcome message element with ID 'welcome-msg' to appear	Welcome message visible on page	Check that welcome message text contains 'Welcome'	PASS
7	Navigates back to login page to test next CSV row	Browser at login page ready for next input	—	PASS
8	Repeats steps 2-7 for each row in CSV file	All CSV rows processed with login attempts	All welcome messages verified for each login	PASS
9	Test ends and browser closes	Browser closed, test finished	—	PASS

Failure Scenario

Failing Condition: Welcome message element not found or text does not contain 'Welcome' after login

Execution Trace Quiz - 3 Questions

What does the test do after clicking the login button?

A Closes the browser

B Immediately navigates back to the login page

C Waits for the welcome message element to appear

D Reads the next CSV row before checking login

Key Result

Using external CSV files for test data helps run multiple test cases easily and keeps test code clean and maintainable.

Practice

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

easy

A. It allows running tests with multiple sets of data without changing the code.

B. It makes the test run faster by using CSV format.

C. It automatically fixes bugs in the test code.

D. It encrypts the test data for security.

Solution

1. Step 1: Understand the purpose of external test data

   Using CSV files lets you separate test data from test code, making tests flexible.

2. Step 2: Identify the benefit in test execution

   With CSV, you can run the same test multiple times with different inputs easily.

3. Final Answer:

   It allows running tests with multiple sets of data without changing the code. -> Option A

4. Quick Check:

   CSV externalizes data = flexible tests [OK]

Hint: CSV stores data separately for easy test reuse [OK]

Common Mistakes:

• Thinking CSV speeds up test execution
• Believing CSV fixes code bugs automatically
• Assuming CSV encrypts data

2. Which Python code snippet correctly opens a CSV file named data.csv for reading test data?

easy

A. file = open('data.csv', 'w')

B. file = open('data.csv', 'r')

C. file = open('data.csv', 'a')

D. file = open('data.csv')

Solution

1. Step 1: Identify the correct file mode for reading

   To read a file, use mode 'r' which stands for read-only.

2. Step 2: Check the options

   file = open('data.csv', 'r') uses 'r' mode correctly; others use write ('w'), append ('a'), or default mode which may not be explicit.

3. Final Answer:

   file = open('data.csv', 'r') -> Option B

4. Quick Check:

   Read mode = 'r' [OK]

Hint: Use 'r' mode to open files for reading [OK]

Common Mistakes:

• Using 'w' which overwrites the file
• Using 'a' which appends instead of reading
• Not specifying mode explicitly

3. Given the CSV file users.csv with content:

username,password
alice,pass123
bob,secure456

What will the output of this code be?

import csv
with open('users.csv', 'r') as file:
    reader = csv.reader(file)
    for row in reader:
        print(row)

medium

A. ('username', 'password')
('alice', 'pass123')
('bob', 'secure456')

B. username,password
alice,pass123
bob,secure456

C. Error: csv.reader cannot read files

D. ['username', 'password']
['alice', 'pass123']
['bob', 'secure456']

Solution

1. Step 1: Understand csv.reader output

   csv.reader reads each line as a list of strings split by commas.

2. Step 2: Analyze the print output

   Each row prints as a list, so header and data rows print as lists of strings.

3. Final Answer:

   ['username', 'password'] ['alice', 'pass123'] ['bob', 'secure456'] -> Option D

4. Quick Check:

   csv.reader returns lists per row [OK]

Hint: csv.reader returns list of strings per row [OK]

Common Mistakes:

• Expecting strings instead of lists
• Confusing tuples with lists
• Thinking csv.reader raises error on valid files

4. What is wrong with this code snippet that reads CSV data for Selenium tests?

import csv
file = open('testdata.csv')
reader = csv.reader(file)
for row in reader:
    print(row)
file.close()

medium

A. The file is not opened in read mode explicitly.

B. The file is not closed after reading.

C. Using open() without a context manager can cause resource leaks.

D. csv.reader cannot be used with open() function.

Solution

1. Step 1: Check file handling best practices

   Using open() without 'with' can cause the file to remain open if errors occur.

2. Step 2: Identify the issue in the code

   Though file.close() is called, if an error happens before, file may not close properly.

3. Final Answer:

   Using open() without a context manager can cause resource leaks. -> Option C

4. Quick Check:

   Use 'with' to auto-close files [OK]

Hint: Always use 'with' to open files safely [OK]

Common Mistakes:

• Thinking file.close() always prevents leaks
• Believing csv.reader can't work with open()
• Ignoring explicit read mode is optional

5. You want to run a Selenium test multiple times using usernames and passwords stored in credentials.csv. Which code snippet correctly reads the CSV and uses the data in a test function?

hard

A. import csv
with open('credentials.csv', 'r') as file:
reader = csv.DictReader(file)
for row in reader:
username = row['username']
password = row['password']
test_login(username, password)

B. import csv
file = open('credentials.csv', 'r')
reader = csv.reader(file)
for row in reader:
test_login(row[0], row[1])
file.close()

C. import csv
with open('credentials.csv') as file:
reader = csv.reader(file)
for row in reader:
test_login(row['username'], row['password'])

D. import csv
with open('credentials.csv', 'r') as file:
reader = csv.reader(file)
for row in reader:
test_login(row[0], row[1])

Solution

1. Step 1: Choose correct CSV reading method for named columns

   csv.DictReader reads CSV rows as dictionaries with column names as keys.

2. Step 2: Use dictionary keys to access username and password

   Accessing row['username'] and row['password'] matches CSV headers and passes correct data.

3. Final Answer:

   Using csv.DictReader and accessing row['username'] and row['password'] correctly. -> Option A

4. Quick Check:

   DictReader + keys = clean data access [OK]

Hint: Use csv.DictReader for named column access [OK]

Common Mistakes:

• Using csv.reader but accessing row by keys
• Not closing files without 'with' block
• Forgetting to specify read mode explicitly