[Django]-Django formset unit test

In particular, I’ve found that the ManagmentForm validator is looking for the following items to be POSTed:

form_data = {
            'form-TOTAL_FORMS': 1, 
            'form-INITIAL_FORMS': 0 
}

It is in fact easy to reproduce whatever is in the formset by inspecting the context of the response.

Consider the code below (with self.client being a regular test client):

url = "some_url"

response = self.client.get(url)
self.assertEqual(response.status_code, 200)

# data will receive all the forms field names
# key will be the field name (as "formx-fieldname"), value will be the string representation.
data = {}

# global information, some additional fields may go there
data['csrf_token'] = response.context['csrf_token']

# management form information, needed because of the formset
management_form = response.context['form'].management_form
for i in 'TOTAL_FORMS', 'INITIAL_FORMS', 'MIN_NUM_FORMS', 'MAX_NUM_FORMS':
    data['%s-%s' % (management_form.prefix, i)] = management_form[i].value()

for i in range(response.context['form'].total_form_count()):
    # get form index 'i'
    current_form = response.context['form'].forms[i]

    # retrieve all the fields
    for field_name in current_form.fields:
        value = current_form[field_name].value()
        data['%s-%s' % (current_form.prefix, field_name)] = value if value is not None else ''

# flush out to stdout
print '#' * 30
for i in sorted(data.keys()):
    print i, '\t:', data[i]

# post the request without any change
response = self.client.post(url, data)

Important note

If you modify data prior to calling the self.client.post, you are likely mutating the DB. As a consequence, subsequent call to self.client.get might not yield to the same data, in particular for the management form and the order of the forms in the formset (because they can be ordered differently, depending on the underlying queryset). This means that

• if you modify data[form-3-somefield] and call self.client.get, this same field might appear in say data[form-8-somefield],
• if you modify data prior to a self.client.post, you cannot call self.client.post again with the same data: you have to call a self.client.get and reconstruct data again.

Django formset unit test

You can add following test helper methods to your test class [Python 3 code]

def build_formset_form_data(self, form_number, **data):
    form = {}
    for key, value in data.items():
        form_key = f"form-{form_number}-{key}"
        form[form_key] = value
    return form

def build_formset_data(self, forms, **common_data):
    formset_dict = {
        "form-TOTAL_FORMS": f"{len(forms)}",
        "form-MAX_NUM_FORMS": "1000",
        "form-INITIAL_FORMS": "1"
    }
    formset_dict.update(common_data)
    for i, form_data in enumerate(forms):
        form_dict = self.build_formset_form_data(form_number=i, **form_data)
        formset_dict.update(form_dict)
    return formset_dict

And use them in test

def test_django_formset_post(self):
    forms = [{"key1": "value1", "key2": "value2"}, {"key100": "value100"}]
    payload = self.build_formset_data(forms=forms, global_param=100)
    print(payload)
    # self.client.post(url=url, data=payload)

You will get correct payload which makes Django ManagementForm happy

{
    "form-INITIAL_FORMS": "1",
    "form-TOTAL_FORMS": "2",
    "form-MAX_NUM_FORMS": "1000",
    "global_param": 100,
    "form-0-key1": "value1",
    "form-0-key2": "value2",
    "form-1-key100": "value100",
}

Profit

There are several very useful answers here, e.g. pymen‘s and Raffi‘s, that show how to construct properly formatted payload for a formset post using the test client.

However, all of them still require at least some hand-coding of prefixes, dealing with existing objects, etc., which is not ideal.

As an alternative, we could create the payload for a post() using the response obtained from a get() request:

def create_formset_post_data(response, new_form_data=None):
    if new_form_data is None:
        new_form_data = []
    csrf_token = response.context['csrf_token']
    formset = response.context['formset']
    prefix_template = formset.empty_form.prefix  # default is 'form-__prefix__'
    # extract initial formset data
    management_form_data = formset.management_form.initial
    form_data_list = formset.initial  # this is a list of dict objects
    # add new form data and update management form data
    form_data_list.extend(new_form_data)
    management_form_data['TOTAL_FORMS'] = len(form_data_list)
    # initialize the post data dict...
    post_data = dict(csrf_token=csrf_token)
    # add properly prefixed management form fields
    for key, value in management_form_data.items():
        prefix = prefix_template.replace('__prefix__', '')
        post_data[prefix + key] = value
    # add properly prefixed data form fields
    for index, form_data in enumerate(form_data_list):
        for key, value in form_data.items():
            prefix = prefix_template.replace('__prefix__', f'{index}-')
            post_data[prefix + key] = value
    return post_data

The output (post_data) will also include form fields for any existing objects.

Here’s how you might use this in a Django TestCase:

def test_post_formset_data(self):
    url_path = '/my/post/url/'
    user = User.objects.create()
    self.client.force_login(user)
    # first GET the form content
    response = self.client.get(url_path)
    self.assertEqual(HTTPStatus.OK, response.status_code)
    # specify form data for test
    test_data = [
        dict(first_name='someone', email='someone@email.com', ...),
        ...
    ]
    # convert test_data to properly formatted dict
    post_data = create_formset_post_data(response, new_form_data=test_data)
    # now POST the data
    response = self.client.post(url_path, data=post_data, follow=True)
    # some assertions here
    ...

Some notes:

• Instead of using the 'TOTAL_FORMS' string literal, we could import TOTAL_FORM_COUNT from django.forms.formsets, but that does not seem to be public (at least in Django 2.2).

• Also note that the formset adds a 'DELETE' field to each form if can_delete is True. To test deletion of existing items, you can do something like this in your test:

    ...
    post_data = create_formset_post_data(response)
    post_data['form-0-DELETE'] = True
    # then POST, etc.
    ...
  

• From the source, we can see that there is no need include MIN_NUM_FORM_COUNT and MAX_NUM_FORM_COUNT in our test data:

  MIN_NUM_FORM_COUNT and MAX_NUM_FORM_COUNT are output with the rest of the management form, but only for the convenience of client-side code. The POST value of them returned from the client is not checked.

This doesn’t seem to be a formset at all. Formsets will always have some sort of prefix on every POSTed value, as well as the ManagementForm that Bartek mentions. It might have helped if you posted the code of the view you’re trying to test, and the form/formset it uses.

My case may be an outlier, but some instances were actually missing a field set in the stock “contrib” admin form/template leading to the error

“ManagementForm data is missing or has been tampered with”

when saved.

The issue was with the unicode method (SomeModel: [Bad Unicode data]) which I found investigating the inlines that were missing.

The lesson learned is to not use the MS Character Map, I guess. My issue was with vulgar fractions (¼, ½, ¾), but I’d assume it could occur many different ways. For special characters, copying/pasting from the w3 utf-8 page fixed it.

postscript-utf-8