pytest-api-cov

A pytest plugin that measures API endpoint coverage for FastAPI and Flask applications. Know which endpoints are tested and which are missing coverage.

Features

• Zero Configuration: Plug-and-play with Flask/FastAPI apps - just install and run
• Client-Based Discovery: Automatically extracts app from your existing test client fixtures
• Terminal Reports: Rich terminal output with detailed coverage information
• JSON Reports: Export coverage data for CI/CD integration

Quick Start

Installation

pip install pytest-api-cov

Basic Usage

For most projects, no configuration is needed, just add the flag to your pytest command:

pytest --api-cov-report

App Location Flexibility

Discovery in this plugin is client-based: the plugin extracts the application instance from your test client fixtures, or from an app fixture when present. This means the plugin integrates with the test clients or fixtures you already use in your tests rather than relying on background file scanning.

How discovery works (in order):

1. OpenAPI Spec: If an OpenAPI spec file is configured (via CLI or config), endpoints are discovered directly from the spec. This takes precedence over app-based discovery.
2. Client Fixtures: If no spec is provided, the plugin looks for configured client fixtures and extracts the app from them.
3. App Fixture: If no client fixture is found, the plugin looks for a standard app fixture.
4. Skip: If none of the above are found, coverage tracking is skipped.

Example

Given this FastAPI app in app.py:

from fastapi import FastAPI

app = FastAPI()

@app.get("/")
def read_root():
    return {"message": "Hello World"}

@app.get("/users/{user_id}")
def get_user(user_id: int):
    return {"user_id": user_id}

@app.post("/users")
def create_user(user: dict):
    return {"message": "User created", "user": user}

@app.get("/health")
def health_check():
    return {"status": "ok"}

And this test file:

def test_root_endpoint(coverage_client):
    response = coverage_client.get("/")
    assert response.status_code == 200

def test_get_user(coverage_client):
    response = coverage_client.get("/users/123")
    assert response.status_code == 200

def test_create_user(coverage_client):
    response = coverage_client.post("/users", json={"name": "John"})
    assert response.status_code == 200

Running pytest --api-cov-report produces:

API Coverage Report
Uncovered Endpoints:
  ❌ GET    /health

Total API Coverage: 75.0%

Or running with advanced options:

pytest --api-cov-report --api-cov-show-covered-endpoints --api-cov-exclusion-patterns="/users*" --api-cov-show-excluded-endpoints --api-cov-report-path=api_coverage.json

API Coverage Report
Uncovered Endpoints:
  ❌ GET    /health
Covered Endpoints:
  ✅ GET    /
Excluded Endpoints:
  🚫 GET    /users/{user_id}
  🚫 POST   /users

Total API Coverage: 50.0%

JSON report saved to api_coverage.json

See examples

# Print an example pyproject.toml configuration snippet
pytest-api-cov show-pyproject

# Print an example conftest.py for a known app module
pytest-api-cov show-conftest FastAPI src.main app

OpenAPI Specification Support

You can use an OpenAPI specification file (JSON or YAML) as the source of truth for API endpoints. This is useful if your app structure makes automatic discovery difficult, or if you want to ensure coverage against a defined contract.

Usage

# Use an OpenAPI spec file
pytest --api-cov-report --api-cov-openapi-spec=openapi.yaml

Or in pyproject.toml:

[tool.pytest_api_cov]
openapi_spec = "openapi.json"

When an OpenAPI spec is provided:

• Endpoints are loaded from the spec file.
• App-based discovery is skipped (unless the spec yields no endpoints).
• Coverage is calculated against the endpoints defined in the spec.

HTTP Method-Aware Coverage

By default, pytest-api-cov tracks coverage for each HTTP method separately. This means GET /users and POST /users are treated as different endpoints for coverage purposes.

Method-Aware (Default Behavior)

Covered Endpoints:
  ✅ GET    /users/{id}
  ✅ POST   /users
Uncovered Endpoints:
  ❌ PUT    /users/{id}
  ❌ DELETE /users/{id}

Total API Coverage: 50.0%  # 2 out of 4 method-endpoint combinations

Endpoint Grouping

To group all methods by endpoint, use:

pytest --api-cov-report --api-cov-group-methods-by-endpoint

Or in pyproject.toml:

[tool.pytest_api_cov]
group_methods_by_endpoint = true

This would show:

Covered Endpoints:
  ✅ /users/{id}  # Any method tested
  ✅ /users       # Any method tested

Total API Coverage: 100.0%  # All endpoints have at least one method tested

Advanced Configuration

Manual Configuration

Create a conftest.py file to specify your app location (works with any file path or structure):

import pytest

# Import from anywhere in your project
from my_project.backend.api import flask_app
# or from src.services.web_server import fastapi_instance  
# or from deeply.nested.modules import my_app

@pytest.fixture
def app():
    return flask_app  # Return your app instance

This approach works with any project structure - the plugin doesn't care where your app is located as long as you can import it.

Custom Test Client Fixtures

The plugin can wrap existing test client fixtures automatically. Recent changes allow you to specify one or more candidate fixture names (the plugin will try them in order) instead of a single configured name.

Default client fixture names the plugin will look for (in order):

• client
• test_client
• api_client
• app_client

If you use a different fixture name, you can provide one or more names via the CLI flag --api-cov-client-fixture-names (repeatable) or in pyproject.toml under [tool.pytest_api_cov] as client_fixture_names (a list).

Option 1: Configuration-Based (recommended for most users)

Configure one or more existing fixture names to be discovered and wrapped automatically by the plugin.

Example pyproject.toml:

[tool.pytest_api_cov]
# Provide a list of candidate fixture names the plugin should try (order matters)
client_fixture_names = ["my_custom_client"]

Or use the CLI flag multiple times:

pytest --api-cov-report --api-cov-client-fixture-names=my_custom_client --api-cov-client-fixture-names=another_fixture

If the configured fixture(s) are not found, the plugin will try to use an app fixture (if present) to create a tracked client. If neither is available or the plugin cannot extract the app from a discovered client fixture, the tests will still run — coverage will simply be unavailable and a warning will be logged.

Option 2: Helper Function

Use the create_coverage_fixture helper to create a custom fixture name:

# conftest.py
import pytest
from pytest_api_cov.plugin import create_coverage_fixture

# Create a new fixture with custom name
my_client = create_coverage_fixture('my_client')

# Or wrap an existing fixture
@pytest.fixture
def original_flask_client():
    from flask.testing import FlaskClient
    from your_app import app
    return app.test_client()

flask_client = create_coverage_fixture('flask_client', 'original_flask_client')

def test_endpoint(my_client):
    response = my_client.get("/endpoint")
    assert response.status_code == 200

def test_with_flask_client(flask_client):
    response = flask_client.get("/endpoint")
    assert response.status_code == 200

The helper returns a pytest fixture you can assign to a name in conftest.py.

Configuration Options

Add configuration to your pyproject.toml:

[tool.pytest_api_cov]
# Fail if coverage is below this percentage
fail_under = 80.0

# Control what's shown in reports
show_uncovered_endpoints = true
show_covered_endpoints = false
show_excluded_endpoints = false

# Exclude endpoints from coverage using wildcard patterns with negation support
# Use * for wildcard matching, all other characters are matched literally
# Use ! at the start to negate a pattern (include what would otherwise be excluded)
# Optionally prefix a pattern with one or more HTTP methods to target only those methods,
exclusion_patterns = [
    "/health",
    "/metrics",
    "/docs/*",
    "/admin/*",
    "!/admin/public",
    "GET,POST /users/*"
]

# Save detailed JSON report
report_path = "api_coverage.json"

# Force Unicode symbols in output
force_sugar = true

# Force no Unicode symbols in output
force_sugar_disabled = true

# Provide candidate fixture names (in priority order).
client_fixture_names = ["my_custom_client"]

# Group HTTP methods by endpoint for legacy behavior (default: false)
group_methods_by_endpoint = false

Notes on exclusion patterns

• Method prefixes (optional): If a pattern starts with one or more HTTP method names followed by whitespace, the pattern applies only to those methods. Methods may be comma-separated and are matched case-insensitively. Example: GET,POST /users/*.
• Path-only patterns (default): If no method is specified the pattern applies to all methods for the matching path (existing behaviour).
• Wildcards: Use * to match any characters in the path portion (not a regex; dots and other characters are treated literally unless * is used).
• Negation: Prefix a pattern with ! to override earlier exclusions and re-include a path (or method-specific path). Negations can also include method prefixes (e.g. !GET /admin/health).
• Matching: Patterns are tested against both the full METHOD /path string and the /path portion to remain compatible with existing configurations.

Examples (pyproject or CLI):

• Exclude the /health path for all methods:

exclusion_patterns = ["/health"]

• Exclude only GET requests to /health:

exclusion_patterns = ["GET /health"]

• Exclude GET and POST for /users/* but re-include GET /users/42:

exclusion_patterns = ["GET,POST /users/*", "!GET /users/42"]

Or using the CLI flags (repeatable):

pytest --api-cov-report --api-cov-exclusion-patterns="GET,POST /users/*" --api-cov-exclusion-patterns="!GET /users/42"

Command Line Options

# Basic coverage report
pytest --api-cov-report

# Set coverage threshold to fail test session
pytest --api-cov-report --api-cov-fail-under=80

# Show covered endpoints
pytest --api-cov-report --api-cov-show-covered-endpoints

# Show excluded endpoints
pytest --api-cov-report --api-cov-show-excluded-endpoints

# Hide uncovered endpoints
pytest --api-cov-report --api-cov-show-uncovered-endpoints=false

# Save JSON report
pytest --api-cov-report --api-cov-report-path=api_coverage.json

# Exclude specific endpoints (supports wildcards and negation)
pytest --api-cov-report --api-cov-exclusion-patterns="/health" --api-cov-exclusion-patterns="/docs/*"

# Specify one or more existing client fixture names (repeatable)
pytest --api-cov-report --api-cov-client-fixture-names=my_custom_client --api-cov-client-fixture-names=another_fixture

# Verbose logging (shows discovery process)
pytest --api-cov-report -v

# Debug logging (very detailed)
pytest --api-cov-report -vv

# Group HTTP methods by endpoint (legacy behavior)
pytest --api-cov-report --api-cov-group-methods-by-endpoint

# Use OpenAPI spec for discovery
pytest --api-cov-report --api-cov-openapi-spec=openapi.yaml

Framework Support

Works automatically with FastAPI, Flask, and Flask-OpenAPI3 applications.

FastAPI

from fastapi import FastAPI

app = FastAPI()

@app.get("/items/{item_id}")
def read_item(item_id: int):
    return {"item_id": item_id}

# Tests automatically get a 'coverage_client' fixture
def test_read_item(coverage_client):
    response = coverage_client.get("/items/42")
    assert response.status_code == 200

Flask

from flask import Flask

app = Flask(__name__)

@app.route("/users/<int:user_id>")
def get_user(user_id):
    return {"user_id": user_id}

# Tests automatically get a 'coverage_client' fixture  
def test_get_user(coverage_client):
    response = coverage_client.get("/users/123")
    assert response.status_code == 200

Parallel Testing

pytest-api-cov fully supports pytest-xdist for parallel test execution:

# Run tests in parallel with coverage
pytest --api-cov-report -n auto

Coverage data is automatically collected from all worker processes and merged in the final report.

JSON Report Format

When using --api-cov-report-path, the plugin generates a detailed JSON report:

{
  "status": 0,
  "coverage": 66.67,
  "required_coverage": 80.0,
  "total_endpoints": 3,
  "covered_count": 2,
  "uncovered_count": 1,
  "excluded_count": 0,
  "detail": [
    {
      "endpoint": "/",
      "callers": ["test_root_endpoint"]
    },
    {
      "endpoint": "/users/{user_id}",
      "callers": ["test_get_user"]
    },
    {
      "endpoint": "/health",
      "callers": []
    }
  ]
}

CI/CD Integration

Fail on Low Coverage

# Fail the build if coverage is below 80%
pytest --api-cov-report --api-cov-fail-under=80

GitHub Actions Example

name: API Coverage
on: [push, pull_request]

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
    - uses: actions/checkout@v4
    - uses: actions/setup-python@v4
      with:
        python-version: '3.12'
    - run: pip install pytest pytest-api-cov
    - run: pytest --api-cov-report --api-cov-fail-under=80 --api-cov-report-path=coverage.json
    - uses: actions/upload-artifact@v4
      with:
        name: api-coverage-report
        path: coverage.json

Troubleshooting

No App Found

If coverage is not running because the plugin could not locate an app, check the following:

• Ensure you are running pytest with --api-cov-report enabled.
• Confirm you have a test client fixture (e.g. client, test_client, api_client) or an app fixture in your test suite.
• If you use a custom client fixture, add its name to client_fixture_names in pyproject.toml or pass it via the CLI using --api-cov-client-fixture-names (repeatable) so the plugin can find and wrap it.
• If the plugin finds the client fixture but cannot extract the underlying app (for example the client type is not supported or wrapped in an unexpected way), you will see a message like "Could not extract app from client" — in that case either provide an app fixture directly or wrap your existing client using create_coverage_fixture.

No endpoints Discovered

If you still see no endpoints discovered:

1. Check that your app is properly instantiated inside the fixture or client.
2. Verify your routes/endpoints are defined and reachable by the test client.
3. Ensure the coverage_client fixture is being used in your tests (or that your configured client fixture is listed and discovered).
4. Use -v or -vv for debug logging to see why the plugin skipped discovery or wrapping.

Framework Not Detected

The plugin supports:

• FastAPI: Detected by FastAPI class
• Flask: Detected by Flask class
• FlaskOpenAPI3: Detected by OpenAPI class (from flask_openapi3 module)

Other frameworks are not currently supported.

License

This project is licensed under the Apache License 2.0.