Django - how to write test for DRF ImageField

Question

I have the following serializer:

from rest_framework.serializers import Serializer, ImageField

class MySerializer(Serializer):
    avatar = ImageField()

how can I write a unit test for it? I used the Django TestCase, but it raises an error.

from django.test import TestCase

class MySerializerTest(TestCase):

    def setUp(self):
        self.data = {}
        ...

    def test_image(self):
        import tempfile
        self.data['avatar'] = tempfile.NamedTemporaryFile(suffix=".jpg").file
        r_data = json.dumps(self.data)
        j_data = json.loads(r_data)
        serializer = MySerializer(data=j_data)
        if not serializer.is_valid():
            import pprint
            pprint.pprint(serializer.errors)
        self.assertEqual(serializer.is_valid(), True)

but it raises the following error:

TypeError: Object of type 'BufferedRandom' is not JSON serializable

What's my mistake? how can I write a test for image field?

score 5 · Accepted Answer · edited May 28 '19 at 14:24

5

I suggest to use SimpleUploadedFile class from django and create and image using Pillow package. See the example below.

from PIL import Image

from django.core.files.uploadedfile import SimpleUploadedFile
from django.test import TestCase
from django.utils.six import BytesIO


class MySerializerTest(TestCase):
    ...

    def test_image(self):
        image = BytesIO()
        Image.new('RGB', (100, 100)).save(image, 'JPEG')
        image.seek(0)

        self.data['avatar'] = SimpleUploadedFile('image.jpg', image.getvalue())
        serializer = MySerializer(data=self.data)
        self.assertEqual(serializer.is_valid(), True)

edited May 28 '19 at 14:24

Thomas W

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answered May 27 '19 at 05:44

Davit Tovmasyan

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it raises an error again. "TypeError: Object of type 'SimpleUploadedFile' is not JSON serializable" – msln May 28 '19 at 12:02
Do not serialize it to JSON, why do you need that? – Davit Tovmasyan May 28 '19 at 12:09
So, how can i test serializer containing an ImageField? as you see, it's a serializer with an ImageField. I want to write test for it. – msln May 28 '19 at 12:12
As you can see, it's already written in my example. You don't need to pass a JSON string to Serializer, simple dictionary will be enough to make it work. – Davit Tovmasyan May 28 '19 at 12:57
now it raises another error! the error is "'str' object is not serializable". this error is in line "serializer.is_valid()". – msln May 28 '19 at 13:46
please update your question with the latest version of the code, so I can help you – Davit Tovmasyan May 29 '19 at 06:36
thanks. it was my mistake that raised the last error. – msln May 30 '19 at 12:13

score 0 · Answer 2 · answered May 27 '19 at 01:55

Usually when you upload a file you would use the multipart request format, and the view would convert the image into an InMemoryUploadedFile object, and that gets passed into your serializer

So to fix your tests I'd recommend trying:

from PIL import Image
from tempfile import NamedTemporaryFile
from django.conf.files.uploadedfile import InMemoryUploadedFile

...

def test_image(self):
    image = Image.new("RGB", (100, 100))
    with NamedTemporaryFile(suffix=".png", mode="w+b") as tmp_file:
        image.save(tmp_file, format="png")
        tmp_file.seek(0)
        byio = BytesIO(temp_file.read())
        inm_file = InMemoryUploadedFile(
            file=byio,
            field_name="avatar",
            name="testImage.png",
            content_type="image/png",
            size=byio.getbuffer().nbytes,
            charset=None,
        )

        self.data['avatar'] = inm_file
        serializer = MySerializer(data=self.data)
        if not serializer.is_valid():
            import pprint
            pprint.pprint(serializer.errors)
        self.assertEqual(serializer.is_valid(), True)

What this is doing is:

Create an image in memory using PIL.Image
Create a NamedTemporaryFile to store the Image data
Take the NamedTemporaryFile and read into a InMemoryUploadedFile
Pass this InMemoryUploadedFile into the serializer

it raises an error: "TypeError: a bytes-like object is required, not 'InMemoryUploadedFile'" — msln, May 28 '19 at 12:09

Django - how to write test for DRF ImageField

2 Answers2