How to Define request.files['file'] from test function?

I need to test a function that registers a new user to my database and creates a profile image for that user within the file system.

Normally the function runs when a form is submitted passing the name, phone, password...and image to the function.

This function therefore expects request.files['file'] to hold an image.

How to call the function and predefine the value of request.files['file'] as it were holding a .jpg image?

here is my test case without consideration of the image required!

def registering(self, username, email, password, passwordCheck, phone):
    return self.app.post('/registering', data=dict(
        username=username, 
        email=email, 
        password=password, 
        passwordCheck=passwordCheck, 
        phone=phone
    ), follow_redirects=True)


def test_registering(self):
    rv = self.registering('TestUser', 'test@test.com', 'passwordTest', 'passwordTest', '900102030')
    assert 'Registered Successfully' in rv.data