want to right a test for a function

I am writing a web application while learning, I have written a function which receives a file. now I want to write a test function for it.i am using pytest.

in the test function, i will be required to submit a file, I have already checked requests for doing so but i am not getting it. please show some light so i can create a test function for the following given function.

@app.post('/check/<number>')
def file_upload(number):
    u_name = request.forms.get('username')  # accepting username
    time = datetime.datetime.now()
    # type(uploaded) == <class 'bytes'>
    uploaded = request.files.get('upload').file.read()  # uploaded outputs by user
    expected = questions[number].output
    expected = expected.strip()
    uploaded = uploaded.strip()
    ans = (uploaded == expected)
    usernames[u_name].append(Submission(question=number, time=time,
                                        output=uploaded, result=ans))
    if not ans:
        return 'Wrong answer'
    else:
        return 'Solved! Great Job!'

I want 200 response while running the test file.