As shown in the docs:

router.register(r'users', UserViewSet)

The example above would generate the following URL patterns:

URL pattern: ^users/$ Name: 'user-list'
URL pattern: ^users/{pk}/$ Name: 'user-detail'
URL pattern: ^accounts/$ Name: 'account-list'
URL pattern: ^accounts/{pk}/$ Name: 'account-detail'

The url name you seem to want to use then is user-list, but since you used basename='users' it would be users-list so:

    def test_user_view(self):
        response = self.client.get(reverse('users-list'))
        # ...