Reading test data from CSV in Selenium Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of reading CSV test data with Python csv.reader

What will be the output of this code snippet that reads a CSV file and prints each row as a list?

Selenium Python

import csv
with open('testdata.csv', newline='') as csvfile:
    reader = csv.reader(csvfile)
    for row in reader:
        print(row)

A Error: FileNotFoundError

B username,password\nuser1,pass1\nuser2,pass2

C ['username,password', 'user1,pass1', 'user2,pass2']

D [['username', 'password'], ['user1', 'pass1'], ['user2', 'pass2']]

💡 Hint

csv.reader returns each row as a list of strings.

The csv.reader reads the CSV file line by line and splits each line by commas into a list. So each printed row is a list of strings representing the columns.

❓ assertion

intermediate

Correct assertion for CSV test data length

Given a list 'data' read from a CSV file with 3 rows including header, which assertion correctly checks the number of data rows excluding the header?

Selenium Python

data = [['username', 'password'], ['user1', 'pass1'], ['user2', 'pass2']]

A assert len(data) == 2

B assert len(data[1:]) == 3

C assert len(data) - 1 == 2

D assert len(data[1:]) == 1

💡 Hint

Remember to exclude the header row when counting data rows.

The header row is the first element, so data rows are from index 1 onward. len(data) is 3, so len(data) - 1 equals 2 data rows.

❓ locator

advanced

Best locator to find username input for CSV-driven test

In a Selenium test reading usernames from CSV, which locator is best to find the username input field for entering data?

A driver.find_element(By.ID, 'username')

B driver.find_element(By.XPATH, '//input[@name="user"]')

C driver.find_element(By.CLASS_NAME, 'input-field')

D driver.find_element(By.CSS_SELECTOR, 'input[type="text"]')

💡 Hint

ID locators are unique and fast.

Using ID is the most reliable and fastest locator if the element has a unique ID attribute.

🔧 Debug

advanced

Identify error reading CSV with DictReader

What error will this code raise when reading a CSV file missing the header row?

Selenium Python

import csv
with open('testdata_noheader.csv', newline='') as csvfile:
    reader = csv.DictReader(csvfile)
    for row in reader:
        print(row['username'])

A AttributeError: 'NoneType' object has no attribute 'get'

B KeyError: 'username'

C No error, prints usernames

D FileNotFoundError

💡 Hint

DictReader uses the first row as keys by default.

If the CSV file has no header row, DictReader treats the first data row as header keys, so 'username' key is missing and accessing row['username'] raises KeyError.

❓ framework

expert

Best practice for integrating CSV test data in Selenium Python tests

Which approach best integrates CSV test data into Selenium tests for multiple login scenarios?

A Read CSV in test setup, use pytest parametrize to run test with each row

B Hardcode test data in test function, ignore CSV

C Read CSV inside each test method without reuse

D Manually copy CSV data into test assertions

💡 Hint

Use test frameworks features to run tests with multiple data sets.

Using pytest parametrize with CSV data read once in setup allows clean, reusable, and scalable tests for multiple data-driven scenarios.

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