Expected view to be called with a URL keyword argument named "pk"

I'm writing a test for a Django Rest Framework view following closely the testing documentation

Here's my simple test:

def test_patient_detail_api_opens(self):
    factory = APIRequestFactory()
    view =PatientDetailApi.as_view()
    request = factory.get(reverse('api_pacjent', kwargs={'pk' :1}))
    force_authenticate(request, user=self.user)
    response = view(request)
    self.assertEqual(response.status_code, 200)

This test fails with the following message:

AssertionError: Expected view PatientDetailApi to be called with a URL keyword argument named "pk". Fix your URL conf, or set the `.lookup_field` attribute on the view correctly.

I fail to understand why this is happening and how to fix this.

• The pk kwargs is there in the URL,
• according to the docs there's no need to add the lookup-field value explicitly if it defaults to pk,
• the view opens correctly and yet this test fails...

Can somebody please explain why this error occurs?

Here's the relevant code:

the 'main' url.py:

urlpatterns = [
    url(r'^pacjent/', include('pacjent.urls')),
] 

pacjent.urls looks like this:

url(r'^api/szczegoly/(?P<pk>\d+)/$', PatientDetailApi.as_view(), name="api_pacjent"),

And PatientDetailApi is this:

class PatientDetailApi(generics.RetrieveUpdateAPIView):
    model = Patient
    serializer_class = PatientDetailsSerializer
    queryset = Patient.objects.all()

    authentication_classes = (SessionAuthentication, BasicAuthentication)
    permission_classes = (IsAuthenticated,)