How can I test binary file uploading with django-rest-framework's test client?

When testing file uploads, you should pass the stream object into the request, not the data.

This was pointed out in the comments by @arocks

Pass { 'image': file} instead

But that didn't full explain why it was needed (and also didn't match the question). For this specific question, you should be doing

from PIL import Image

class TestFileUpload(APITestCase):

    def test_file_is_accepted(self):
        self.client.force_authenticate(self.user)

        image = Image.new('RGB', (100, 100))

        tmp_file = tempfile.NamedTemporaryFile(suffix='.jpg')
        image.save(tmp_file)
        tmp_file.seek(0)

        response = self.client.post('my_url', {'image': tmp_file}, format='multipart')

       self.assertEqual(status.HTTP_201_CREATED, response.status_code)

This will match a standard Django request, where the file is passed in as a stream object, and Django REST Framework handles it. When you just pass in the file data, Django and Django REST Framework interpret it as a string, which causes issues because it is expecting a stream.

And for those coming here looking to another common error, why file uploads just won't work but normal form data will: make sure to set format="multipart" when creating the request.

This also gives a similar issue, and was pointed out by @RobinElvin in the comments

It was because I was missing format='multipart'

Python 3 users: make sure you open the file in mode='rb' (read,binary). Otherwise, when Django calls read on the file the utf-8 codec will immediately start choking. The file should be decoded as binary not utf-8, ascii or any other encoding.

# This won't work in Python 3
with open(tmp_file.name) as fp:
        response = self.client.post('my_url', 
                                   {'image': fp}, 
                                   format='multipart')

# Set the mode to binary and read so it can be decoded as binary
with open(tmp_file.name, 'rb') as fp:
        response = self.client.post('my_url', 
                                   {'image': fp}, 
                                   format='multipart')

You can use Django built-in SimpleUploadedFile:

from django.core.files.uploadedfile import SimpleUploadedFile

class TestFileUpload(APITestCase):
    ...

    def test_file_is_accepted(self):
        ...

       tmp_file = SimpleUploadedFile(
                      "file.jpg", "file_content", content_type="image/jpg")

       response = self.client.post(
                      'my_url', {'image': tmp_file}, format='multipart')
       self.assertEqual(response.status_code, status.HTTP_201_CREATED)

It's not so simple to understand how to do it if you want to use the PATCH method, but I found the solution in this question.

from django.test.client import BOUNDARY, MULTIPART_CONTENT, encode_multipart

with open(tmp_file.name, 'rb') as fp:
    response = self.client.patch(
        'my_url', 
        encode_multipart(BOUNDARY, {'image': fp}), 
        content_type=MULTIPART_CONTENT
    )

For those in Windows, the answer is a bit different. I had to do the following:

resp = None
with tempfile.NamedTemporaryFile(suffix='.jpg', delete=False) as tmp_file:
    image = Image.new('RGB', (100, 100), "#ddd")
    image.save(tmp_file, format="JPEG")
    tmp_file.close()

# create status update
with open(tmp_file.name, 'rb') as photo:
    resp = self.client.post('/api/articles/', {'title': 'title',
                                               'content': 'content',
                                               'photo': photo,
                                               }, format='multipart')
os.remove(tmp_file.name)

The difference, as pointed in this answer (https://stackoverflow.com/a/23212515/72350), the file cannot be used after it was closed in Windows. Under Linux, @Meistro's answer should work.