pyproject.toml configuration in PyTest - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of pytest with custom testpaths in pyproject.toml

Given this pyproject.toml configuration, what will pytest discover and run?

PyTest

[tool.pytest.ini_options]
testpaths = ["tests/integration", "tests/unit"]

A Pytest runs tests in all folders including 'tests/integration' and 'tests/unit'.

B Pytest runs tests in all folders except 'tests/integration' and 'tests/unit'.

C Pytest runs tests only in the root folder, ignoring subfolders.

D Pytest runs tests only in 'tests/integration' and 'tests/unit' folders.

💡 Hint

The testpaths option limits where pytest looks for tests.

The testpaths setting in pyproject.toml tells pytest to only look for tests inside the specified folders. Here, only 'tests/integration' and 'tests/unit' are included.

❓ assertion

intermediate

Correct assertion for pytest capturing output

You want to check that your function prints 'Hello World' when run. Which pytest assertion correctly tests this using capsys?

PyTest

def greet():
    print("Hello World")

def test_greet(capsys):
    greet()
    captured = capsys.readouterr()
    # Which assertion below is correct?

A assert captured.err == "Hello World\n"

B assert captured.out == "Hello World"

C assert captured.out == "Hello World\n"

D assert captured.out.contains("Hello World")

💡 Hint

Remember print adds a newline character at the end.

When using capsys, captured.out contains stdout including newlines. The print function adds a newline, so the output ends with '\n'.

❓ locator

advanced

Identify the correct pytest marker configuration in pyproject.toml

Which pyproject.toml snippet correctly registers a custom marker named 'slow' with a description?

A

[tool.pytest.ini_options]
markers = "slow: marks tests as slow to run"

B

[tool.pytest.ini_options]
markers = ["slow: marks tests as slow to run"]

C

[tool.pytest.ini_options]
markers = {slow = "marks tests as slow to run"}

D

[tool.pytest.ini_options]
markers = slow: marks tests as slow to run

💡 Hint

Markers must be a list of strings with 'name: description' format.

The markers option expects a list of strings, each string describing a marker name and its purpose separated by a colon.

🔧 Debug

advanced

Why does pytest ignore tests in a subfolder despite pyproject.toml settings?

You set testpaths = ["tests"] in pyproject.toml, but pytest does not find tests in tests/api. What is the most likely cause?

A The test files in <code>tests/api</code> do not start with 'test_' or end with '_test.py'.

B The <code>pyproject.toml</code> file is not in the project root directory.

C The <code>tests/api</code> folder lacks an __init__.py file, so pytest skips it.

D Pytest requires explicit inclusion of subfolders in <code>testpaths</code>.

💡 Hint

Pytest discovers tests by file name patterns by default.

Pytest looks for test files matching patterns like 'test_*.py' or '*_test.py'. If files in 'tests/api' do not follow this, pytest ignores them even if the folder is included.

❓ framework

expert

Effect of adding 'addopts' in pyproject.toml on pytest runs

Given this pyproject.toml snippet, what is the effect of the addopts option when running pytest?

PyTest

[tool.pytest.ini_options]
addopts = "-v --maxfail=2"

A Pytest runs in verbose mode and stops after 2 test failures.

B Pytest runs with 2 workers in parallel and verbose output.

C Pytest runs with verbose output and retries failed tests twice.

D Pytest runs with maximum 2 tests executed and verbose output.

💡 Hint

The --maxfail option limits how many failures stop the test run.

The addopts option adds command-line arguments to every pytest run. Here, -v enables verbose output, and --maxfail=2 stops testing after two failures.

Practice

1. What is the main purpose of the pyproject.toml file in pytest?

easy

A. To store pytest configuration settings in one place

B. To write test functions directly

C. To install pytest dependencies

D. To generate test reports automatically

Solution

1. Step 1: Understand the role of pyproject.toml

   This file is used to keep configuration settings for pytest centralized.

2. Step 2: Differentiate from other files

   It does not contain test code or install dependencies but configures how pytest runs.

3. Final Answer:

   To store pytest configuration settings in one place -> Option A

4. Quick Check:

   Configuration file [OK]

Hint: Remember: pyproject.toml holds settings, not test code [OK]

Common Mistakes:

• Confusing configuration file with test code file
• Thinking it installs packages
• Assuming it generates reports automatically

2. Which of the following is the correct way to specify the test paths in pyproject.toml for pytest?

easy

A. [pytest]
testpaths = "tests"

B. [tool.pytest]
testpaths = ["tests"]

C. [tool.pytest]
test_paths = ["tests"]

D. [tool.pytest]
paths = "tests"

Solution

1. Step 1: Identify correct section header

   pytest settings go under [tool.pytest] in pyproject.toml.

2. Step 2: Check correct key and value format

   The key is testpaths and it expects a list of strings, e.g., ["tests"].

3. Final Answer:

   [tool.pytest] testpaths = ["tests"] -> Option B

4. Quick Check:

   Section and key names must be exact [OK]

Hint: Use [tool.pytest] and testpaths as a list [OK]

Common Mistakes:

• Using wrong section header like [pytest]
• Using wrong key names like test_paths
• Assigning string instead of list for testpaths

3. Given this pyproject.toml snippet:

[tool.pytest]
markers = ["slow: marks tests as slow"]
addopts = "-v --maxfail=2"

What happens when you run pytest?

medium

A. Tests run verbosely but do not stop on failures; 'slow' marker ignored

B. Tests run silently and stop after 2 failures; 'slow' marker ignored

C. Tests run verbosely and stop after 2 failures; 'slow' marker is recognized

D. Tests run silently and continue on failures; 'slow' marker recognized

Solution

1. Step 1: Understand addopts settings

   The -v flag makes output verbose; --maxfail=2 stops tests after 2 failures.

2. Step 2: Understand markers setting

   Defining slow marker means pytest recognizes it and can filter or mark tests accordingly.

3. Final Answer:

   Tests run verbosely and stop after 2 failures; 'slow' marker is recognized -> Option C

4. Quick Check:

   Verbose + maxfail + marker recognized [OK]

Hint: addopts controls run options; markers define test tags [OK]

Common Mistakes:

• Ignoring that -v means verbose output
• Not knowing --maxfail stops after failures
• Assuming markers are ignored without explicit use

4. You wrote this in pyproject.toml:

[tool.pytest]
markers = "slow: marks slow tests"
addopts = -v

What is the problem when running pytest?

medium

A. addopts ignored but markers work

B. No error; configuration works fine

C. Markers ignored but addopts works

D. Syntax error because markers should be a list, and addopts needs quotes

Solution

1. Step 1: Check markers format

   Markers must be a list of strings, but here it is a single string without brackets.

2. Step 2: Check addopts format

   addopts value must be a string in quotes; here it is unquoted, causing syntax error.

3. Final Answer:

   Syntax error because markers should be a list, and addopts needs quotes -> Option D

4. Quick Check:

   Lists need brackets; strings need quotes [OK]

Hint: Always use brackets for lists and quotes for strings in TOML [OK]

Common Mistakes:

• Writing markers as a plain string instead of list
• Forgetting quotes around string values
• Assuming pytest ignores bad config silently

5. You want pytest to automatically run tests only in the integration_tests folder and recognize a custom marker api. Which pyproject.toml configuration is correct?

hard

A. [tool.pytest]
testpaths = ["integration_tests"]
markers = ["api: marks API tests"]

B. [tool.pytest]
testpaths = "integration_tests"
markers = "api: marks API tests"

C. [pytest]
testpaths = ["integration_tests"]
markers = ["api"]

D. [tool.pytest]
paths = ["integration_tests"]
markers = ["api: marks API tests"]

Solution

1. Step 1: Set correct testpaths key and value

   Use testpaths as a list under [tool.pytest] to specify test folders.

2. Step 2: Define markers properly

   Markers must be a list of strings describing each marker with a colon and description.

3. Final Answer:

   [tool.pytest] testpaths = ["integration_tests"] markers = ["api: marks API tests"] -> Option A

4. Quick Check:

   Correct keys, list format, and section [OK]

Hint: Use [tool.pytest], testpaths list, and markers list with descriptions [OK]

Common Mistakes:

• Using string instead of list for testpaths
• Wrong section header like [pytest]
• Markers missing description or wrong format