Retry mechanism for flaky tests in Selenium Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this retry decorator on flaky test?

Consider this Python code using Selenium and a retry decorator for flaky tests. What will be printed when the test function is run?

Selenium Python

import random

def retry(times):
    def decorator(func):
        def wrapper():
            for attempt in range(1, times + 1):
                try:
                    func()
                    print(f"Test passed on attempt {attempt}")
                    break
                except Exception as e:
                    print(f"Attempt {attempt} failed: {e}")
                    if attempt == times:
                        print("Test failed after retries")
        return wrapper
    return decorator

@retry(3)
def flaky_test():
    if random.choice([True, False]):
        raise Exception("Random failure")

flaky_test()

A Test passed on attempt 3

B Attempt 1 failed: Random failure\nTest passed on attempt 2

C Test passed on attempt 1

D Attempt 1 failed: Random failure\nAttempt 2 failed: Random failure\nAttempt 3 failed: Random failure\nTest failed after retries

💡 Hint

The test stops retrying once it passes.

The retry decorator runs the test up to 3 times. If the test passes on the first try, it prints 'Test passed on attempt 1' and stops retrying.

❓ assertion

intermediate

Which assertion correctly verifies retry count in flaky test?

You want to assert that a flaky Selenium test retried exactly 3 times before failing. Which assertion code snippet correctly checks this?

Selenium Python

retry_attempts = []

def flaky_test():
    retry_attempts.append(1)
    raise Exception("Fail")

# Retry decorator calls flaky_test 3 times

# Which assertion below is correct?

A assert retry_attempts == 3

B assert len(retry_attempts) == 3

C assert retry_attempts.count == 3

D assert retry_attempts.length == 3

💡 Hint

retry_attempts is a list, check its length.

len(retry_attempts) returns the number of times the test was retried. The other options use invalid syntax or methods.

🔧 Debug

advanced

Why does this retry decorator not retry on failure?

This retry decorator is supposed to retry a flaky Selenium test 3 times, but it only runs once. What is the bug?

Selenium Python

def retry(times):
    def decorator(func):
        def wrapper():
            for attempt in range(times):
                try:
                    func()
                    print(f"Passed on attempt {attempt}")
                    return
                except Exception:
                    print(f"Failed on attempt {attempt}")
        return wrapper
    return decorator

@retry(3)
def flaky_test():
    raise Exception("Fail")

flaky_test()

A The decorator is missing @functools.wraps

B The range(times) should start at 1, not 0

C The exception is not caught properly

D The 'return' inside try block stops retries after first attempt

💡 Hint

Check what happens when the test passes or fails inside the loop.

The 'return' inside the try block exits the wrapper function immediately after first attempt, so no retries happen.

❓ framework

advanced

Which pytest feature best supports retrying flaky Selenium tests?

You want to automatically retry flaky Selenium tests in pytest without writing custom decorators. Which pytest feature or plugin should you use?

A pytest-rerunfailures plugin

B pytest-mock plugin

C pytest-cov plugin

D pytest-xdist plugin

💡 Hint

Look for a plugin that reruns failed tests.

pytest-rerunfailures reruns failed tests automatically. The others serve different purposes.

🧠 Conceptual

expert

What is the main risk of using retry mechanisms for flaky Selenium tests?

Retrying flaky Selenium tests can hide underlying problems. What is the biggest risk of relying heavily on retries?

A Masking real issues and reducing test suite reliability

B Increasing test execution speed significantly

C Making tests easier to maintain and debug

D Guaranteeing 100% test pass rate

💡 Hint

Think about what happens if flaky tests are ignored by retries.

Retries can hide real bugs or environment issues, making the test suite less trustworthy.

Practice

1. What is the main purpose of a retry mechanism in Selenium tests?

easy

A. To permanently ignore failed tests without rerunning

B. To speed up test execution by running tests in parallel

C. To rerun tests that fail due to temporary issues like slow loading

D. To generate detailed logs for every test step

Solution

1. Step 1: Understand flaky tests

   Flaky tests fail sometimes due to temporary problems like slow page loads or network delays.

2. Step 2: Purpose of retry mechanism

   Retry mechanism reruns failed tests to check if failure was temporary, reducing false failures.

3. Final Answer:

   To rerun tests that fail due to temporary issues like slow loading -> Option C

4. Quick Check:

   Retry mechanism = rerun flaky tests [OK]

Hint: Retry fixes temporary failures by rerunning tests [OK]

Common Mistakes:

• Thinking retry speeds up tests
• Assuming retry ignores failures
• Confusing retry with logging

2. Which of the following is the correct way to implement a simple retry decorator in Python for Selenium tests?

easy

A. def retry(func):
try:
func()
except Exception:
func()

B. def retry(func):
def wrapper():
for _ in range(3):
try:
return func()
except Exception:
pass
return wrapper

C. def retry(func):
while True:
func()
return func

D. def retry(func):
for _ in range(3):
func()
return func

Solution

1. Step 1: Check retry decorator structure

   def retry(func): def wrapper(): for _ in range(3): try: return func() except Exception: pass return wrapper defines a wrapper function that tries to run the test 3 times catching exceptions.

2. Step 2: Verify retry logic correctness

   def retry(func): def wrapper(): for _ in range(3): try: return func() except Exception: pass return wrapper retries on exception and returns on success, which is correct retry behavior.

3. Final Answer:

   def retry(func): def wrapper(): for _ in range(3): try: return func() except Exception: pass return wrapper -> Option B

4. Quick Check:

   Retry decorator = try 3 times with exception catch [OK]

Hint: Retry decorator wraps function with try-except loop [OK]

Common Mistakes:

• Not catching exceptions inside loop
• Infinite loops without exit
• Calling function multiple times without try-except

3. Given this retry decorator and test function, what will be printed?

def retry(func):
    def wrapper():
        for i in range(2):
            try:
                return func()
            except Exception:
                print(f"Retry {i+1} failed")
        print("All retries failed")
    return wrapper

@retry
def test():
    print("Running test")
    raise Exception("Fail")

test()

medium

A. Running test
Retry 1 failed
Running test
Retry 2 failed
All retries failed

B. Running test
All retries failed

C. Running test
Retry 1 failed
Retry 2 failed

D. Running test
Retry 1 failed
Running test
Retry 2 failed

Solution

1. Step 1: Analyze retry loop

   The wrapper tries to run test twice. Each time test() prints "Running test" then raises Exception.

2. Step 2: Trace output

   On first try, prints "Running test", then exception triggers "Retry 1 failed". Second try repeats same steps, then prints "Retry 2 failed". After loop ends, prints "All retries failed".

3. Final Answer:

   Running test Retry 1 failed Running test Retry 2 failed All retries failed -> Option A

4. Quick Check:

   Retry prints on each failure, then final failure message [OK]

Hint: Each retry prints failure message, then final failure after loop [OK]

Common Mistakes:

• Missing repeated 'Running test' print
• Ignoring final 'All retries failed' print
• Assuming retry stops after first failure

4. You wrote this retry decorator but it does not retry on failure. What is the bug?

def retry(func):
    def wrapper():
        for _ in range(3):
            try:
                func()
            except Exception:
                continue
    return wrapper

medium

A. The decorator is missing the @functools.wraps(func) call

B. The except block should raise the exception instead of continue

C. The loop should be a while loop instead of for loop

D. The function does not return the result or stop retrying on success

Solution

1. Step 1: Check retry logic

   The wrapper calls func() but never returns its result or breaks loop on success.

2. Step 2: Effect of missing return

   Without return, wrapper always completes loop and returns None, so retry never stops on success.

3. Final Answer:

   The function does not return the result or stop retrying on success -> Option D

4. Quick Check:

   Missing return causes always 3 retries even on success [OK]

Hint: Always return on success to stop retries [OK]

Common Mistakes:

• Not returning function result inside try
• Misusing continue in except block
• Ignoring decorator metadata preservation

5. You want to implement a retry mechanism in Selenium tests that retries up to 3 times with a 2-second delay between tries. Which code snippet correctly implements this?

hard

A. import time

def retry(func):
def wrapper():
for i in range(3):
try:
return func()
except Exception:
if i < 2:
time.sleep(2)
else:
raise
return wrapper

B. import time

def retry(func):
def wrapper():
for _ in range(3):
try:
func()
except Exception:
time.sleep(2)
return wrapper

C. def retry(func):
def wrapper():
try:
return func()
except Exception:
time.sleep(2)
return func()
return wrapper

D. import time

def retry(func):
def wrapper():
while True:
try:
return func()
except Exception:
time.sleep(2)
return wrapper

Solution

1. Step 1: Check retry count and delay

   import time def retry(func): def wrapper(): for i in range(3): try: return func() except Exception: if i < 2: time.sleep(2) else: raise return wrapper retries 3 times with a 2-second sleep between tries except after last attempt.

2. Step 2: Verify exception handling

   import time def retry(func): def wrapper(): for i in range(3): try: return func() except Exception: if i < 2: time.sleep(2) else: raise return wrapper raises exception after last retry, correctly stopping retries on failure.

3. Final Answer:

   import time def retry(func): def wrapper(): for i in range(3): try: return func() except Exception: if i < 2: time.sleep(2) else: raise return wrapper -> Option A

4. Quick Check:

   Retry with delay and raise after last try [OK]

Hint: Use loop with sleep and raise after last retry [OK]

Common Mistakes:

• Not raising exception after last retry
• Missing delay between retries
• Retrying infinitely without limit