FastAPI Custom Datetime Format (ISO 8601)

test_fast_api_custom_datetime.py

import asyncio
from datetime import datetime

import pytest
from fastapi import FastAPI
from starlette.testclient import TestClient
from pydantic import BaseModel


class CustomDatetime(BaseModel):
    dt_field: datetime

    class Config:
        json_encoders = {
            datetime: lambda dt: dt.strftime('%Y-%m-%dT%H:%M:%SZ'),
        }


app = FastAPI()


@pytest.fixture(autouse=True)
def get_event_loop() -> None:
    asyncio.set_event_loop(asyncio.new_event_loop())


@app.get('/model', response_model=CustomDatetime)
def get_model():
    return CustomDatetime(dt_field=datetime(2019, 1, 1, 8))


def test_datetime_custom_format():
    with TestClient(app) as client:
        response = client.get('/model')
    assert response.json() == {'dt_field': '2019-01-01T08:00:00Z'}