Test independence in PyTest - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Why is test independence important?

Imagine you have multiple tests for a calculator app. Why should each test be independent from others?

A Because tests should share data to reduce code duplication.

B So that one test's failure doesn't cause others to fail, making debugging easier.

C To make tests run slower and use more resources.

D To ensure tests always run in a fixed order.

💡 Hint

Think about how one broken test might affect others if they depend on each other.

Test independence means tests do not rely on each other's results or data. This helps isolate failures and makes debugging easier.

❓ Predict Output

intermediate

What is the output of these pytest tests?

Consider these two pytest tests that share a global variable. What will be the test results?

PyTest

counter = 0

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

def test_increment_again():
    global counter
    counter += 1
    assert counter == 1

A Both tests fail

B Both tests pass

C test_increment fails, test_increment_again passes

D test_increment passes, test_increment_again fails

💡 Hint

Think about the value of counter when each test runs.

The first test sets counter to 1 and passes. The second test runs after and increments counter to 2, so the assertion counter == 1 fails.

🔧 Debug

advanced

Identify the cause of flaky tests due to shared state

These pytest tests sometimes fail randomly. What is the main cause?

PyTest

shared_list = []

def test_add_item():
    shared_list.append(1)
    assert 1 in shared_list

def test_clear_list():
    shared_list.clear()
    assert shared_list == []

A Tests share mutable global state causing interference between tests.

B Tests use different assert statements causing confusion.

C Tests do not import pytest properly.

D Tests run in parallel causing race conditions.

💡 Hint

Look at the variable shared_list and how it is used.

Both tests modify the same global list. If test_add_item runs before test_clear_list, the list is cleared. But if order changes, tests may fail unpredictably.

❓ framework

advanced

How to ensure test independence in pytest?

Which pytest feature helps to create independent tests by providing fresh data for each test?

A Using global variables to share data between tests.

B Running tests in a fixed order using <code>pytest-order</code> plugin.

C Using fixtures with <code>scope='function'</code> to provide fresh setup for each test.

D Disabling assertions to speed up tests.

💡 Hint

Think about how pytest can prepare data or state before each test runs.

Fixtures with function scope run before each test, giving a clean environment and avoiding shared state.

❓ assertion

expert

Which assertion best checks test independence in pytest?

You want to verify that a test does not affect global state. Which assertion is best?

PyTest

global_state = {'count': 0}

def test_modify_state():
    global_state['count'] += 1
    # Which assertion below best ensures test independence?

A assert global_state['count'] == 0

B assert global_state['count'] > 0

C assert isinstance(global_state, dict)

D assert global_state != {}

💡 Hint

Think about what value count should have if tests are independent.

If tests are independent, the global count should reset to 0 before each test. Checking it equals 0 ensures no leftover changes.