How to use Coverage/Unit Testing in FastAPI using PyTest

pip install pytest

To verify that PyTest has been successfully installed, you can use the following command to check the version:

pytest --version

To customize the behavior, we can create a file named pytest.ini or setup.cfg in our project directory and specify configuration options.

[pytest]
testpaths = tests
addopts = -v

Create test cases for your FastAPI endpoints. Use PyTest’s assert statements to validate responses. Here’s an example:

# tests/test_main.py
from fastapi.testclient import TestClient
from app.main import app
 
client = TestClient(app)
 
def test_read_main():
    response = client.get("/")
    assert response.status_code == 200
    assert response.json() == {"message": "Hello Dolly!"}

To run test:

pytest

Writing Unit Tests for FastAPI Endpoints

GET endpoint:

from fastapi.testclient import TestClient
from app.main import app
 
client = TestClient(app)
 
def test_read_item():
    response = client.get("/items/1")
    assert response.status_code == 200
    assert response.json() == {"id": 1, "name": "Item1"}

POST endpoint:

def test_create_item():
    data = {"name": "New Item"}
    response = client.post("/items/", json=data)
    assert response.status_code == 201
    assert response.json()["name"] == "New Item"

PUT endpoint:

def test_update_item():
    data = {"name": "Updated Item"}
    response = client.put("/items/1", json=data)
    assert response.status_code == 200
    assert response.json()["name"] == "Updated Item"

DELETE endpoint:

def test_delete_item():
    response = client.delete("/items/1")
    assert response.status_code == 204

Integrating coverage testing with PyTest:

Integrating coverage testing with PyTest in FastAPI projects is essential for assessing the effectiveness of test suites and identifying areas that require additional testing. Here’s how to incorporate FastAPI testing with PyTest seamlessly:

To integrate coverage testing with PyTest, you can use the pytest-cov plugin. First, install the plugin using pip:

pip install pytest-cov

Next, run your PyTest tests with coverage enabled:

pytest --cov=<modulename_or_packagename> tests/

In the above command, replace <modulename_or_packagename> with the module name or package, you want to measure coverage for. PyTest will execute the tests and collect coverage data for the module or package. After running the tests, PyTest will generate a coverage report displaying the code coverage percentage for each module or package. You can view the coverage report in the terminal or generate an HTML report for a more detailed analysis:

pytest --cov=<module_or_package> --cov-report=html tests/

Interpreting coverage results involves more than just looking at the percentage. Focus on understanding which parts of your code are covered and which are not. Prioritize testing for critical components, edge cases, and error-handling logic to improve coverage in areas that matter most.

In order to improve coverage results, consider writing additional tests to cover untested code paths. This will include error cases, boundary conditions, and edge cases. Refactor the code to make it more easier for testing of individual components. Regularly review coverage reports and adjust testing strategies based on feedback to continuously enhance code coverage and overall test effectiveness.By integrating test coverage tools with PyTest and adopting strategies for interpreting and improving coverage results, developers can ensure comprehensive test coverage and maintain high code quality in FastAPI projects. This approach aligns with quality assurance in FastAPI and ensures that the development team uses effective testing methodologies.