Multiple file upload testing

[Adam Fletcher]

Hi DRFers,

I've got two simple serializers:

class ImportFileSerializer(serializers.Serializer):
    file_to_import = serializers.FileField()

class ImportFilesSerializer(serializers.Serializer):
    files = serializers.ListField(child=ImportFileSerializer())

I can test the single-file upload pretty easily:

    def test_import_single_file_valid_everything(self) -> None:

        filename="foo.csv"

        client = APIClient()
        url = hosts_reverse("import_file-list")
        client.login(username=self.user.username, password="xxxxxxxxx")
        with open(f"{filename}", "rb") as csvfile:
            # patch
            response = client.post(
                url,
                {
                    "file_to_import": csvfile,
                    "file_name": filename,
                },
                format="multipart",
            )
            self.assertEqual(response, success_response)

And my single-file upload view loves this - it does a `ImportFileSerializer(data=request.data)` and an is_valid() check and I can get the file, etc. 

BUT. My multiple file test doesn't work (the other code is the same as the above test):

        file_names = [ "foo1", "foo2", "foo3" ]
        post_body = {}
        post_body["files"] = []
        for filename in file_names:
            with open(f"{filename}", "rb") as csvfile:
                post_body["files"].append({
                    "file_to_import": csvfile,
                    "file_name": filename,
                })

        response = client.post(
            url, post_body,
            format="multipart",
        )

My ImportFilesSerializer passes the is_valid() check but returns an empty list for the validated_data. Any idea why? 

Thanks!

-Adam