Parallel test execution in Testing Fundamentals - Build an Automation Script

Run two simple tests in parallel and verify both pass

Preconditions (2)

Step 1: Create two test functions: test_addition and test_subtraction

Step 2: In test_addition, assert that 2 + 3 equals 5

Step 3: In test_subtraction, assert that 5 - 3 equals 2

Step 4: Run both tests in parallel using pytest with the -n 2 option

✅ Expected Result: Both tests run at the same time and pass successfully

Automation Requirements - pytest with pytest-xdist

Assertions Needed:

Assert 2 + 3 == 5 in test_addition

Assert 5 - 3 == 2 in test_subtraction

Best Practices:

Use pytest fixtures if needed for setup

Use pytest-xdist for parallel execution

Keep tests independent to avoid interference

Use clear and simple assertions

Automated Solution

Testing Fundamentals

import pytest


def test_addition():
    assert 2 + 3 == 5


def test_subtraction():
    assert 5 - 3 == 2

# To run these tests in parallel, use the command:
# pytest -n 2

This script defines two simple test functions using pytest. Each test checks a basic math operation with an assertion.

We use pytest -n 2 to run both tests at the same time in parallel using the pytest-xdist plugin.

This approach helps speed up test execution by running tests concurrently. The tests are independent, so they do not affect each other.

Common Mistakes - 3 Pitfalls

{'mistake': 'Running tests sequentially without using pytest-xdist', 'why_bad': 'Tests run one after another, so no speed benefit from parallel execution.', 'correct_approach': "Install pytest-xdist and run tests with 'pytest -n 2' to enable parallel execution."}

Writing tests that share state or data without isolation

Using print statements instead of assertions

Bonus Challenge

Now add a third test for multiplication and run all three tests in parallel

Show Hint

Practice

1. What is the main benefit of parallel test execution in software testing?

easy

A. It automatically fixes bugs found during testing.

B. It ensures tests run one after another to avoid conflicts.

C. It runs multiple tests at the same time to save testing time.

D. It slows down tests to check for memory leaks.

Solution

1. Step 1: Understand parallel execution purpose

   Parallel test execution means running tests simultaneously, not sequentially.

2. Step 2: Identify the main benefit

   Running tests at the same time saves overall testing time and speeds feedback.

3. Final Answer:

   It runs multiple tests at the same time to save testing time. -> Option C

4. Quick Check:

   Parallel execution = faster testing [OK]

Hint: Parallel means tests run together, saving time [OK]

Common Mistakes:

• Confusing parallel with sequential execution
• Thinking parallel fixes bugs automatically
• Assuming parallel slows down tests

2. Which of the following is the correct way to enable parallel test execution in a test framework configuration?

easy

A. enableParallelExecution = false

B. runTestsSequentially = true

C. testMode = singleThread

D. parallel = true

Solution

1. Step 1: Identify enabling parallel execution

   Setting parallel = true typically enables parallel runs in configs.

2. Step 2: Check other options

   Options A, B, and D disable or prevent parallel execution.

3. Final Answer:

   parallel = true -> Option D

4. Quick Check:

   Enable parallel = true [OK]

Hint: Look for 'parallel = true' to enable parallel runs [OK]

Common Mistakes:

• Using flags that disable parallel execution
• Confusing sequential and parallel settings
• Misreading boolean values

3. Consider this pseudocode for running tests in parallel:

start test1
start test2
wait for test1
wait for test2
print('All tests done')

What will be the output if both tests pass quickly?

medium

A. test1
test2

B. All tests done

C. Error: tests cannot run in parallel

D. No output

Solution

1. Step 1: Understand parallel start

   Both tests start without waiting, so they run at the same time.

2. Step 2: Wait for both tests to finish

   The code waits for test1 and test2 to complete before printing.

3. Final Answer:

   All tests done -> Option B

4. Quick Check:

   Wait then print = 'All tests done' [OK]

Hint: Wait for all tests before printing output [OK]

Common Mistakes:

• Assuming output prints before tests finish
• Thinking tests run sequentially
• Expecting test names printed automatically

4. You configured parallel test execution but notice tests fail due to shared data conflicts. What is the best way to fix this?

medium

A. Make tests independent by avoiding shared data or using separate data copies.

B. Run tests sequentially instead of parallel.

C. Ignore failures as they are caused by parallelism.

D. Increase the number of parallel threads.

Solution

1. Step 1: Identify cause of failure

   Failures happen because tests share data and interfere with each other.

2. Step 2: Fix by isolating tests

   Making tests independent or using separate data copies avoids conflicts.

3. Final Answer:

   Make tests independent by avoiding shared data or using separate data copies. -> Option A

4. Quick Check:

   Isolate tests to fix conflicts [OK]

Hint: Avoid shared data to fix parallel test conflicts [OK]

Common Mistakes:

• Ignoring failures caused by data conflicts
• Just reducing parallel threads without fixing data
• Assuming parallel always works without changes

5. You have 10 independent tests that each take 1 minute to run sequentially. Your test framework supports running 5 tests in parallel. How long will the total test run take if you use parallel execution correctly?

hard

A. 2 minutes

B. 5 minutes

C. 10 minutes

D. 1 minute

Solution

1. Step 1: Calculate sequential time

   Running 10 tests one by one takes 10 minutes (10 x 1 minute).

2. Step 2: Calculate parallel batches

   With 5 tests running at once, tests run in 2 batches (10 / 5 = 2).

3. Step 3: Calculate total parallel time

   Each batch takes 1 minute, so total time is 2 minutes.

4. Final Answer:

   2 minutes -> Option A

5. Quick Check:

   10 tests / 5 parallel = 2 minutes [OK]

Hint: Divide tests by parallel threads for total time [OK]

Common Mistakes:

• Assuming parallel time equals single test time
• Multiplying instead of dividing tests by threads
• Ignoring batch count in calculation