Improved List/NonNull of_type exceptions and tests. Fixed #337

graphene/types/structures.py

@@ -9,6 +9,15 @@ class Structure(UnmountedType):
 
     def __init__(self, of_type, *args, **kwargs):
         super(Structure, self).__init__(*args, **kwargs)
+        if not isinstance(of_type, Structure) and isinstance(of_type, UnmountedType):
+            cls_name = type(self).__name__
+            of_type_name = type(of_type).__name__
+            raise Exception("{} could not have a mounted {}() as inner type. Try with {}({}).".format(
+                cls_name,
+                of_type_name,
+                cls_name,
+                of_type_name,
+            ))
         self.of_type = of_type
 
     def get_type(self):
@@ -56,7 +65,7 @@ class NonNull(Structure):
         super(NonNull, self).__init__(*args, **kwargs)
         assert not isinstance(self.of_type, NonNull), (
             'Can only create NonNull of a Nullable GraphQLType but got: {}.'
-        ).format(type)
+        ).format(self.of_type)
 
     def __str__(self):
         return '{}!'.format(self.of_type)

graphene/types/tests/test_structures.py

@@ -10,12 +10,51 @@ def test_list():
     assert str(_list) == '[String]'
 
 
+def test_list_with_unmounted_type():
+    with pytest.raises(Exception) as exc_info:
+        List(String())
+    
+    assert str(exc_info.value) == 'List could not have a mounted String() as inner type. Try with List(String).'
+
+
+def test_list_inherited_works_list():
+    _list = List(List(String))
+    assert isinstance(_list.of_type, List)
+    assert _list.of_type.of_type == String
+
+
+def test_list_inherited_works_nonnull():
+    _list = List(NonNull(String))
+    assert isinstance(_list.of_type, NonNull)
+    assert _list.of_type.of_type == String
+
+
 def test_nonnull():
     nonnull = NonNull(String)
     assert nonnull.of_type == String
     assert str(nonnull) == 'String!'
 
 
+def test_nonnull_inherited_works_list():
+    _list = NonNull(List(String))
+    assert isinstance(_list.of_type, List)
+    assert _list.of_type.of_type == String
+
+
+def test_nonnull_inherited_dont_work_nonnull():
+    with pytest.raises(Exception) as exc_info:
+        NonNull(NonNull(String))
+    
+    assert str(exc_info.value) == 'Can only create NonNull of a Nullable GraphQLType but got: String!.'
+
+
+def test_nonnull_with_unmounted_type():
+    with pytest.raises(Exception) as exc_info:
+        NonNull(String())
+    
+    assert str(exc_info.value) == 'NonNull could not have a mounted String() as inner type. Try with NonNull(String).'
+
+
 def test_list_comparasion():
     list1 = List(String)
     list2 = List(String)