pyproject.toml configuration in PyTest - Build an Automation Script

Configure pytest using pyproject.toml and verify test discovery

Preconditions (2)

Step 1: Create a pyproject.toml file in the project root

Step 2: Add pytest configuration section to pyproject.toml to set test paths and markers

Step 3: Run pytest from the command line without additional arguments

Step 4: Observe pytest discovers and runs the test_sample.py test

Step 5: Verify pytest output shows the test passed

✅ Expected Result: pytest discovers tests according to pyproject.toml settings and runs them successfully with a passing result

Automation Requirements - pytest

Assertions Needed:

Verify pytest exit code is 0 (success)

Verify output contains the test function name

Verify output shows tests passed

Best Practices:

Use pyproject.toml for pytest configuration instead of command line flags

Keep test files named with test_ prefix for automatic discovery

Use pytest's built-in assertion introspection

Automated Solution

PyTest

[tool.pytest.ini_options]
testpaths = ["tests"]
markers = ["smoke: quick smoke tests"]

# test_sample.py file content

def test_example():
    assert 1 + 1 == 2

# To run the test, execute in terminal:
# pytest

# The test will be discovered in the 'tests' folder as configured in pyproject.toml

# Sample command line output expected:
# ============================= test session starts =============================
# collected 1 item
#
# tests/test_sample.py .                                                     [100%]
#
# ============================== 1 passed in 0.01s ==============================

The pyproject.toml file configures pytest to look for tests in the tests folder and defines a custom marker smoke. This replaces the need to pass command line options each time.

The test_sample.py file contains a simple test function test_example that asserts 1 + 1 equals 2.

Running pytest in the terminal will automatically discover tests in the tests folder as specified, run them, and show the results.

This setup follows best practices by centralizing configuration and using pytest's default discovery conventions.

Common Mistakes - 3 Pitfalls

Not placing pyproject.toml in the project root directory

Using incorrect section name in pyproject.toml (e.g., [pytest] instead of [tool.pytest.ini_options])

{'mistake': "Not naming test files or functions with the 'test_' prefix", 'why_bad': 'pytest will not discover tests automatically, causing zero tests to run', 'correct_approach': "Name test files and functions starting with 'test_' to enable automatic discovery"}

Bonus Challenge

Now add a custom marker 'slow' in pyproject.toml and write two tests, one marked 'slow' and one normal. Run pytest to only execute the normal tests.

Show Hint

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