class ChangePasswordView(UpdateAPIView):

    serializer_class = ChangePasswordSerializer
    model = UserInfo
    permission_classes = (IsAuthenticated,)

    def get(self, request, *args, **kwargs):
        return Response(status=200)

    def put(self, request, *args, **kwargs):
        self.object = self.request.user
        serializer = self.get_serializer(data=request.data)

        if serializer.is_valid():
            if not self.object.check_password(serializer.data.get("old_password")):
                return Response(
                    {"old_password": ["Wrong password"]},
                    status=400
                )
            self.object.set_password(serializer.data.get("new_password"))
            self.object.save()
            return Response("Success", status=200)

        return Response(serializer.errors, status=400)

def test_change_password(self):
    client = APIClient()
    self.client.post('/api/user/login/', self.data, follow=True)
    self.client.login(username="testuser", password="secret")
    request = client.put('/api/user/change_password/', self.new_data)

    self.assertEqual(
         request, '<Response status_code=200, "application/json">'
    )

def setUp(self):
    self.data = {
        'username': 'testuser',
        'password': 'secret'
    }

    self.new_data = {
        'old_password': 'secret',
        'new_password': 'other_secret'
    }

    User.objects.create_user(**self.data)

from rest_framework import status

class ChangePasswordView(UpdateAPIView):

serializer_class = ChangePasswordSerializer
model = UserInfo
permission_classes = (IsAuthenticated,)

def get(self, request, *args, **kwargs):
    return Response(status=status.HTTP_200_OK)

def post(self, request, *args, **kwargs):
    user = request.user
    serializer = self.get_serializer(data=request.data)

    if serializer.is_valid():
        if not self.object.check_password(serializer.data.get("old_password")):
            msg = _("Wrong old password.")
            raise ValidationError(msg)

        user.set_password(serializer.data.get("new_password"))
        user.save()
        return Response("Success", status=status.HTTP_200_OK)

    msg = _('Something went wrong while reading the passwords')
    raise ValidationError(msg)

from rest_framework import status

def test_change_password(self):
    client = APIClient()
    self.client.post('/api/user/login/', self.data, follow=True)
    self.client.login(username="testuser", password="secret")
    response = self.post('/api/user/change_password/', self.new_data)

    self.assertEqual(response.status_code, status.HTTP_200_OK)