Fake post request for unit testing in flask

I am working on a web app using flask and postgresql. I am wrting unit tests for all my view functions. However, I look up the doc and some other stackoverflow posts like this for testing post request and it doesn't work.

This is a method in a class inherited from unittest.TestCase

def test__student_receive_data(self):
        built_in_ids = populate_db()
        role_student = query_role('Student')
        student = query_user(built_in_ids['student_id'])
        student.role = role_student
        lab = query_lab(built_in_ids['lab_id'])
        experiment = query_experiment(built_in_ids['experiment_id'])
        self.login(student.username, student.password)

        # Start a new session
        student = query_user(student.id)
        student.labs.append(lab)
        ds.commit()

        observationsForOneExperiment = [{'labId': lab.id,
                                         'experimentName': experiment.name,
                                         'observation': randlength_word()}]
        observationsGroupByStudent = [{'studentName': student.name,
                                      'observationsForOneExperiment': observationsForOneExperiment}]
        data_to_be_sent = dict(observationsGroupByStudent=observationsGroupByStudent)
        cprint(json.dumps(data_to_be_sent))
        rv = self.app.post('/_student_receive_data', data=json.dumps(data_to_be_sent), follow_redirects=True)
        self.assertEqual(rv.status_code, 200)

This is a view function which receives post request from the test function above

# store incoming data into the database
@app.route('/_student_receive_data', methods=['POST'])
@permission_required(m.Permission.DATA_ENTRY)
def _student_receive_data():
    # get data from client
    jsonData = request.get_json()
    print(current_user)
    print(jsonData)
    print(request.form)
    # check that data is in the appropriate format
    err_msg = check_existence(jsonData, 'observationsGroupByStudent')
    if err_msg != '':
        return err_json(err_msg)
    err_msg = add_observations_sent_by_students(jsonData['observationsGroupByStudent'])
    if err_msg != '':
        return err_json(err_msg)
    return normal_json(jsonData)

The print out in the terminal(Clearly, nothing is received):

User<id: pip, username: pip, password: pip, role: Student, classes: ['bio101_16fall'], labs: ['test_bio101_amy']>
None
ImmutableMultiDict([])