Django - how to write test for DRF ImageField - django

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?

Answer 1

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)

Answer 2

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