This is a simple proof of concept demonstrating how I like to handle files during tests.

test_image_and_file_field.py

"""
This is a simple proof of concept demonstrating how I like to handle files during tests.

Setup
-----

    wget http://hbn.link/1NoLHf0
    virtualenv .venv
    source .venv/bin/activate
    pip install django django-inmemorystorage


Usage
-----

    python test_image_and_file_field.py


How it works
------------

The script will:

1. setup a single file django project with an in-memory database;
2. create the models Document and Animal;
3. make sure each model has a database table;
4. run our test case.
"""
from django.conf import settings
from django.db import models, connection, utils
from django.test import TestCase, override_settings
from django.core.files.uploadedfile import SimpleUploadedFile


# Configure Django if needed.
if not settings.configured:
    from pathlib import Path
    from django import setup

    settings.configure(
        DATABASES=dict(default=dict(ENGINE='django.db.backends.sqlite3', NAME=':memory:')),
        ROOT_URLCONF=Path(__file__).stem,
        SECRET_KEY='secret'
    )

    setup()


# Declare the model
class Document(models.Model):
    blob = models.FileField()
    __module__ = 'app.models'  # hack to trick Django

    class Meta:
        app_label = 'app'  # Compensate for the hack above.


class Animal(models.Model):
    picture = models.ImageField()
    __module__ = 'app.models'  # hack to trick Django

    class Meta:
        app_label = 'app'  # Compensate for the hack above.


# Make sure model has a table.
with connection.schema_editor() as schema_editor:
    for model in (Document, Animal):
        try:
            schema_editor.create_model(model)
        except utils.OperationalError:
            pass  # Ignore if table exists


# Declare tests...

# Tiniest Gif ever: 26 bytes
# source: http://probablyprogramming.com/2009/03/15/the-tiniest-gif-ever
TINY_GIF = b'GIF89a\x01\x00\x01\x00\x00\xff\x00,\x00\x00\x00\x00\x01\x00\x01\x00\x00\x02\x00;'


@override_settings(DEFAULT_FILE_STORAGE='inmemorystorage.InMemoryStorage')
class TestFields(TestCase):
    def test_image_field(self):
        Animal.objects.create(picture=SimpleUploadedFile('tiny.gif', TINY_GIF))
        self.assertTrue(Animal.objects.exists())

    def test_file_field(self):
        Document.objects.create(blob=SimpleUploadedFile('license.txt', 'GPL'.encode()))
        self.assertTrue(Document.objects.exists())


if __name__ == '__main__':
    # Run our test.
    from django.test.runner import DiscoverRunner
    DiscoverRunner().run_tests('', extras=[TestFields])