Testing file uploads in Flask

Question

I\'m using Flask-Testing for my Flask integration tests. I\'ve got a form that has a file upload for a logo that I\'m trying to write tests for but I keep getting an error sayin

Answer 1

You can use Werkzeug's FileStorage (as used by Flask under the hood).

You can mock a file like this:

from werkzeug.datastructures import FileStorage
import io
import json

# Here we are mocking a JSON file called Input.json
my_dict = {"msg": "hello!"}
input_json = json.dumps(my_dict, indent=4).encode("utf-8")

mock_file = FileStorage(
    stream=io.BytesIO(input_json),
    filename="Input.json",
    content_type="application/json",
)

Notice that I use a real file on my server: tests/assets/my_video.mp4

from werkzeug.datastructures import FileStorage


my_video = os.path.join("tests/assets/my_video.mp4")

my_file = FileStorage(
    stream=open(my_video, "rb"),
    filename="my_video.mp4",
    content_type="video/mpeg",
),

rv = client.post(
   "/api/v1/video",
   data={
      "my_video": my_file,
   },
   content_type="multipart/form-data"
)

Test to see it returns a response status code of 200:

assert "200" in rv.status

I can then test that the file arrives in a test directory on the server:

assert "my_video.mp4" in os.listdir("tests/my_test_path")

Also note, you need to set the mocked file to None on teardown otherwise you'll get a ValueError: I/O operation on closed file. . Below is a Pytest example:

    def setup_method(self):
        self.mock_file = FileStorage(
            stream=io.BytesIO(input_json),
            filename="Input.json",
            content_type="application/json",
        )

    def teardown_method(self):
        self.mock_file = None