post.py

# python3 -m pip install fastapi pytest
# python3 -m pytest tests/post.py
from typing import Union

from fastapi import Form, FastAPI, Query
from fastapi.testclient import TestClient

app = FastAPI()

@app.post("/list")
def read_query(q: Union[list[str], list[None]] = Form()):
    return q

@app.post("/none")
def read_none_query(q: Union[list[str], None] = Form()):
    return q

client = TestClient(app)

def test_empty_list_valid():
    response = client.post("/list", data={"q": []})
    assert response.status_code == 200
    assert response.json() == []

def test_full_list_valid():
    response = client.post("/list", data={"q": ["hi", "there"]})
    assert response.status_code == 200
    assert response.json() == ["hi", "there"]

def test_none_empty_list_valid():
    response = client.post("/none", data={"q": []})
    assert response.status_code == 200
    assert response.json() == []

def test_none_full_list_valid():
    response = client.post("/none", data={"q": ["hi", "there"]})
    assert response.status_code == 200
    assert response.json() == ["hi", "there"]