Manually referencing dummy file in Django HttpRequest for testing form submission

Question

In Django, I am trying to create automated tests for a project that includes a file submission via ModelForm. One of the model fields is a FileField, and a test file has already been placed into the project directory so it can be referenced.

In order to test the form submission I am creating a dummy user and manually generating an HttpRequest() containing POST data. However, I am unsure of how to manually insert the file into the FileField portion -- I assume I need to reference it somehow, but I don't know exactly how to do that.

The test is below:

def test_form_submit(self):
        user = User.objects.create_user(
            username="testuser",
            email="[email protected]",
            password="asdfasdf"
        )

        request = HttpRequest()
        request.POST = {
            "file": [insert file here],     # is a FileField
            "name": "Richard",
            "date": "2022-01-28",
            "desc": "A test submission."
        }

        form = FileSubmissionForm(request.POST, user=user)
        form.save()
        self.assertEqual(Submission.objects.count(), 1)

How do I properly reference the file for this test case? The dummy file is located at $MEDIA_ROOT/testing/dummy_file.txt.

Thanks!