How can I simulate a flask request in python to test my program? [duplicate]

import flask


app = flask.Flask(__name__)

@app.route("/")
def main(request: flask.Request):
    if flask.request.method == 'GET':
        try:
            request_json = request.get_json()
        except:
            return '', 400
        else:
            stuff = do_stuff(request_json)
        return stuff, 200

if __name__ == "__main__":
    app.run(debug=True)

HTTP/1.0 400 BAD REQUEST
Content-Type: text/html; charset=utf-8
Content-Length: 0
Server: Werkzeug/2.0.1 Python/3.9.6
Date: Tue, 26 Oct 2021 16:57:19 GMT