Ordering tests for parallel safety in PyTest - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to mark a test to run serially using pytest.

PyTest

import pytest

@pytest.mark.[1]
def test_database_connection():
    assert connect_to_db() is True

Drag options to blanks, or click blank then click option'

Aorder

Bserial_run

Crun_serial

Dserial

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect marker names like 'serial_run' or 'run_serial'.

Trying to use 'order' which is unrelated.

The correct marker to indicate a test should run serially is '@pytest.mark.serial'.

2fill in blank

medium

Complete the code to ensure tests run in a specific order using pytest-ordering.

PyTest

import pytest

@pytest.mark.order([1])
def test_initialize():
    assert setup_environment() is True

Drag options to blanks, or click blank then click option'

A1

B'first'

C'start'

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using strings instead of integers for order.

Starting order from 0 instead of 1.

The '@pytest.mark.order(1)' decorator sets the test to run first in order.

3fill in blank

hard

Fix the error in the test function to avoid parallel execution conflicts.

PyTest

import pytest

@pytest.mark.[1]
def test_modify_shared_resource():
    resource.lock()
    modify_resource()
    resource.unlock()

Drag options to blanks, or click blank then click option'

Aconcurrent

Bparallel

Cserial

Dasync

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'parallel' or 'concurrent' which allow parallel runs.

Using 'async' which is unrelated to test ordering.

Marking the test as 'serial' ensures it does not run in parallel, avoiding conflicts.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that orders tests by priority and skips low priority.

PyTest

test_order = {test: priority for test, priority in tests.items() if priority [1] [2]

Drag options to blanks, or click blank then click option'

A>

B1

C<

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' causing wrong tests to be selected.

Using '1' instead of '0' as threshold.

The comprehension keeps tests with priority greater than 0, skipping low priority tests.

5fill in blank

hard

Fill all three blanks to create a test report dictionary filtering passed tests with duration over 1 second.

PyTest

report = {test['name']: test['duration'] for test in test_results if test['status'] == [1] and test['duration'] [2] [3]

Drag options to blanks, or click blank then click option'

A'passed'

B>

C1

D'failed'

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'failed' instead of 'passed' for status.

Using '<' instead of '>' for duration comparison.

Using 0 or other numbers instead of 1 for duration.

The dictionary includes tests that passed and took longer than 1 second.

Practice

1. Why is it important to order tests when running pytest in parallel?

easy

A. To make tests run slower

B. To avoid conflicts when tests share resources

C. To increase the number of tests

D. To skip tests automatically

Solution

1. Step 1: Understand test resource sharing

   Tests that share resources like files or databases can interfere with each other if run at the same time.

2. Step 2: Recognize the role of ordering

   Ordering tests ensures they run in a sequence that prevents conflicts and errors.

3. Final Answer:

   To avoid conflicts when tests share resources -> Option B

4. Quick Check:

   Ordering prevents resource conflicts [OK]

Hint: Order tests to prevent shared resource conflicts [OK]

Common Mistakes:

• Thinking ordering slows tests down
• Believing ordering increases test count
• Assuming ordering skips tests

2. Which of the following is the correct way to order a test to run third using pytest?

easy

A. @pytest.mark.order(3)

B. @pytest.order(3)

C. @pytest.mark.run(3)

D. @pytest.order_mark(3)

Solution

1. Step 1: Recall pytest ordering syntax

   The correct decorator to order tests is @pytest.mark.order(n) where n is the order number.

2. Step 2: Match the syntax to options

   Only @pytest.mark.order(3) uses the correct decorator @pytest.mark.order(3).

3. Final Answer:

   @pytest.mark.order(3) -> Option A

4. Quick Check:

   Use @pytest.mark.order(n) for ordering [OK]

Hint: Use @pytest.mark.order(n) to set test order [OK]

Common Mistakes:

• Using @pytest.order instead of @pytest.mark.order
• Confusing order with run decorators
• Misspelling the decorator name

3. Given these two tests, what will be the order of execution when run with pytest in parallel with ordering?

import pytest

@pytest.mark.order(2)
def test_second():
    assert True

@pytest.mark.order(1)
def test_first():
    assert True

medium

A. Tests run in random order

B. test_second runs before test_first

C. test_first runs before test_second

D. Tests fail due to ordering conflict

Solution

1. Step 1: Identify order markers

   test_first has order 1, test_second has order 2.

2. Step 2: Understand execution order

   Lower order numbers run before higher ones, so test_first runs before test_second.

3. Final Answer:

   test_first runs before test_second -> Option C

4. Quick Check:

   Lower order number runs first [OK]

Hint: Lower order number runs first in pytest [OK]

Common Mistakes:

• Assuming higher order runs first
• Thinking tests run randomly despite order
• Believing ordering causes test failure

4. You have two tests that share a database. You want to run them in parallel safely. Which of these is a problem in the code below?

import pytest

@pytest.mark.order(1)
def test_write_db():
    # writes data
    assert True

@pytest.mark.order(2)
def test_read_db():
    # reads data
    assert True

medium

A. Tests must have the same order number

B. The order decorators are incorrect syntax

C. Tests are missing assert statements

D. Tests are ordered but may still run in parallel causing conflicts

Solution

1. Step 1: Check ordering usage

   Tests use correct order decorators, so syntax is fine.

2. Step 2: Understand parallel execution impact

   Even with order, if tests run truly in parallel (e.g., with pytest-xdist), they may overlap and cause conflicts.

3. Final Answer:

   Tests are ordered but may still run in parallel causing conflicts -> Option D

4. Quick Check:

   Ordering alone doesn't guarantee parallel safety [OK]

Hint: Ordering doesn't prevent parallel overlap without locks [OK]

Common Mistakes:

• Thinking order decorators fix parallel conflicts
• Believing same order number is required
• Ignoring assert statements importance

5. You have three tests that modify a shared file. To run them safely in parallel, you want to order them and ensure no overlap. Which approach below best achieves this?

hard

A. Use @pytest.mark.order to run tests sequentially and add file locks

B. Remove order decorators and run all tests in parallel without locks

C. Use @pytest.mark.order with the same order number for all tests

D. Run tests without ordering but add random sleep delays

Solution

1. Step 1: Understand test resource sharing

   Tests modifying the same file can cause conflicts if run simultaneously.

2. Step 2: Combine ordering with locking

   Ordering ensures sequence, and file locks prevent overlap during execution.

3. Step 3: Evaluate options

   Use @pytest.mark.order to run tests sequentially and add file locks uses both ordering and locks, which is the safest approach.

4. Final Answer:

   Use @pytest.mark.order to run tests sequentially and add file locks -> Option A

5. Quick Check:

   Order plus locks ensure parallel safety [OK]

Hint: Combine order and locks for safe parallel file tests [OK]

Common Mistakes:

• Relying on order alone without locks
• Using same order number causing race conditions
• Adding random delays instead of proper synchronization