Running FastAPI Tests in ‘Test’ Mode

When developing and testing FastAPI applications, it’s often desirable to run the application in a ‘test’ mode with specific configurations or behaviors. This can help isolate tests, prevent unintended side effects, and streamline the development process.

Creating a Test Configuration

Define a Configuration Model:

Python

from pydantic import BaseModel

class Settings(BaseModel):
debug: bool = True
test_mode: bool = False

Load the Configuration:

Python

from dotenv import load_dotenv
from pathlib import Path

def get_settings():
load_dotenv()
return Settings()

Inject the Configuration into Endpoints:

Python

from fastapi import Depends

def get_settings(settings: Settings = Depends(get_settings)):
return settings

Running Tests in Test Mode

Set the TEST_MODE Environment Variable:

Bash

export TEST_MODE=True

Use the Configuration in Tests:

Python

def test_read_root(client, settings: Settings = Depends(get_settings)):
assert settings.test_mode
# Perform test logic

Conditional Logic in Endpoints

You can use the test_mode flag to conditionally modify the behavior of your endpoints:

Python

@app.get("/")
def read_root(settings: Settings = Depends(get_settings)):
    if settings.test_mode:
        return {"message": "This is test mode"}
    else:
        # Regular endpoint logic

By running FastAPI tests in ‘test’ mode, you can create a controlled environment for testing your application’s functionality, ensuring that it behaves as expected in different scenarios.