Avoiding test interdependence in PyTest - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to mark the test as independent using pytest.

PyTest

import pytest

@pytest.mark.[1]
def test_example():
    assert 1 + 1 == 2

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

Aisolated

Bindependent

Cindep

Dindep_test

Attempts:

3 left

💡 Hint

Common Mistakes

Using a non-existent marker name.

Using abbreviations instead of full marker names.

The correct pytest marker to indicate test independence is independent.

2fill in blank

medium

Complete the code to reset the shared resource before each test using a fixture.

PyTest

import pytest

@pytest.fixture(autouse=True)
def reset_resource():
    global resource
    resource = [1]

resource = 0

def test_increment():
    global resource
    resource += 1
    assert resource == 1

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

A''

BNone

CFalse

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Resetting to None causes type errors.

Using empty string instead of zero.

Resetting the shared resource to 0 ensures tests start fresh.

3fill in blank

hard

Fix the error in the test to avoid dependence on previous test results.

PyTest

def test_append_item():
    items = []
    items.append('apple')
    assert len(items) == [1]

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

A1

B0

C2

DNone

Attempts:

3 left

💡 Hint

Common Mistakes

Assuming the list has previous items from other tests.

Using zero or None as length after append.

After appending one item, the list length should be 1.

4fill in blank

hard

Fill both blanks to create a fixture that provides a fresh list for each test.

PyTest

import pytest

@pytest.fixture

def [1]():
    return [2]

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

Afresh_list

B[]

C{}

Dlist()

Attempts:

3 left

💡 Hint

Common Mistakes

Returning a dictionary instead of a list.

Using a shared list literal that causes test interference.

The fixture named fresh_list returns a new empty list using list() each time.

5fill in blank

hard

Fill all three blanks to write two independent tests using the fresh_list fixture.

PyTest

def test_add_item_[1](fresh_list):
    fresh_list.append('item')
    assert len(fresh_list) == [2]

def test_clear_list_[3](fresh_list):
    fresh_list.clear()
    assert len(fresh_list) == 0

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

Aone

B1

Ctwo

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using the same test name for both tests.

Expecting wrong list length after append.

The first test is named test_add_item_one and expects length 1. The second test is named test_clear_list_two.

Practice

1. Why is it important to avoid test interdependence in pytest?

easy

A. To ensure each test runs independently and results are reliable

B. To make tests run faster by sharing data

C. To reduce the number of test functions needed

D. To allow tests to modify global variables freely

Solution

1. Step 1: Understand test independence

   Tests should not rely on each other to avoid hidden bugs and unclear results.

2. Step 2: Identify the benefit of independence

   Independent tests ensure that a failure in one test does not affect others, making debugging easier.

3. Final Answer:

   To ensure each test runs independently and results are reliable -> Option A

4. Quick Check:

   Test independence = Reliable results [OK]

Hint: Tests must run alone to keep results clear and reliable [OK]

Common Mistakes:

• Thinking tests should share data to run faster
• Believing test order does not matter
• Allowing tests to modify shared global state

2. Which pytest feature helps to avoid test interdependence by preparing fresh data for each test?

easy

A. Using print statements for debugging

B. Using global variables

C. Using fixtures with scope='function'

D. Using assert statements inside tests

Solution

1. Step 1: Identify pytest features for setup

   Fixtures with scope='function' run before each test, providing fresh data.

2. Step 2: Understand why this avoids interdependence

   Fresh data per test prevents tests from affecting each other through shared state.

3. Final Answer:

   Using fixtures with scope='function' -> Option C

4. Quick Check:

   Fixtures with function scope = Fresh data each test [OK]

Hint: Use function-scoped fixtures to reset data per test [OK]

Common Mistakes:

• Using global variables which cause shared state
• Confusing print statements with setup tools
• Thinking assert statements control test independence

3. Given the following pytest code, what will be the output when running both tests?

shared_list = []

def test_add_one():
    shared_list.append(1)
    assert shared_list == [1]

def test_add_two():
    shared_list.append(2)
    assert shared_list == [2]

medium

A. Both tests pass

B. Both tests fail

C. test_add_one fails, test_add_two passes

D. test_add_one passes, test_add_two fails

Solution

1. Step 1: Analyze shared_list state across tests

   shared_list is global and not reset, so after test_add_one it contains [1].

2. Step 2: Check assertions in each test

   test_add_one expects [1] and passes; test_add_two appends 2 making list [1,2], but asserts [2], so it fails.

3. Final Answer:

   test_add_one passes, test_add_two fails -> Option D

4. Quick Check:

   Shared state causes second test failure [OK]

Hint: Global mutable state causes test failures due to leftover data [OK]

Common Mistakes:

• Assuming shared_list resets automatically
• Ignoring order of test execution
• Expecting both tests to pass with shared state

4. Identify the problem in this pytest code that causes test interdependence:

data = {}

def test_set_value():
    data['key'] = 'value'
    assert data['key'] == 'value'

def test_check_empty():
    assert data == {}

medium

A. Using dict instead of list causes errors

B. data dictionary is not reset between tests

C. Tests are missing return statements

D. Assertions are incorrect syntax

Solution

1. Step 1: Examine shared data usage

   data is a global dictionary modified in test_set_value and not cleared before test_check_empty.

2. Step 2: Understand test impact

   test_check_empty expects data to be empty, but it contains {'key': 'value'}, causing failure and interdependence.

3. Final Answer:

   data dictionary is not reset between tests -> Option B

4. Quick Check:

   Shared mutable dict causes test dependency [OK]

Hint: Reset shared data to avoid tests affecting each other [OK]

Common Mistakes:

• Thinking assertions syntax is wrong
• Believing return statements are needed in tests
• Confusing data types with test independence

5. You want to avoid test interdependence in pytest when multiple tests modify a shared database. Which approach is best?

hard

A. Use a fixture that creates a fresh database for each test and cleans up after

B. Share one database instance and reset it manually in one test only

C. Run tests in a specific order so dependencies are met

D. Use global variables to track database state across tests

Solution

1. Step 1: Understand best practice for shared resources

   Creating a fresh database per test ensures no leftover data affects other tests.

2. Step 2: Evaluate other options

   Sharing one instance with manual reset or relying on test order causes hidden dependencies and fragile tests.

3. Final Answer:

   Use a fixture that creates a fresh database for each test and cleans up after -> Option A

4. Quick Check:

   Fresh resource per test = No interdependence [OK]

Hint: Fresh setup and cleanup per test avoids hidden dependencies [OK]

Common Mistakes:

• Relying on test order which is unreliable
• Using global variables causing shared state bugs
• Resetting shared state in only one test