Django REST Framework - 'User' object is not callable (in unit test)

I am currently writing a unit test for the following get_can_edit function in my serializer:

def get_can_edit(self, obj):
    request = self.context.get('request')
    user = User.objects.get(username=request.user)
    return user == obj.admin

In my test, I call the function here:

def test_get_can_edit(self):
    self.request1 = RequestFactory().post('./fake_path')
    self.request1.user = SimpleLazyObject(self.user1)
    self.request1.query_params = {}
    self.serializer1 = ConferenceSerializer(context={'request': self.request1})
    self.canEdit1 = self.serializer1.get_can_edit(self.conference)

When I run the test, it fails the the error: 'User' object is not callable, and references the following line in the serializer get_can_edit function:

user = User.objects.get(username=request.user)

However, when running in browser, the get_can_edit function performs correctly and has no problem with the 'User' objet being callable.

I originally assumed that there was a problem with the format of the fake data I was creating (I'm using factory_boy and RequestFactory to create the fake data). Using a debugger, I went into the get_can_edit function both by calling the test, and through the server by making a real request. In both cases, request.user and obj.admin were in the correct form, so I ruled out a data formatting error.

Next, I tried

User.objects.get(username=request.user)

in the debuggers. It worked for the real request in the server, and returned the same 'User' object is not callable error for the fake request in the test. I did a quick stack overflow/google search for object is not callable errors in Django, but it looked like other cases were solved by making sure a model was imported correctly (mine is definitely imported correctly).

So at this point I know that there's a problem with my test case that does not exist with the real request, but I can't really figure out what it is, and I'm running out of ideas.

Full code:

The serializer

The test

Thanks so much, let me know if there's an easier way to go about this.