update null tests

- add tests from the ref implementation
  https://github.com/graphql/graphql-js/pull/544/files

Author: jaemk

graphql/language/tests/test_parser.py

@@ -94,6 +94,69 @@ def test_allows_null_value():
     parse('{ fieldWithNullableStringInput(input: null) }')
 
 
+def test_parses_null_value_to_null():
+    result = parse('{ fieldWithObjectInput(input: {a: null, b: null, c: "C", d: null}) }')
+    values = result.definitions[0].selection_set.selections[0].arguments[0].value.fields
+    expected = (
+        (u'a', ast.NullValue()),
+        (u'b', ast.NullValue()),
+        (u'c', ast.StringValue(value=u'C')),
+        (u'd', ast.NullValue()),
+    )
+    for name_value, actual in zip(expected, values):
+        assert name_value == (actual.name.value, actual.value)
+
+
+def test_parses_null_value_in_list():
+    result = parse('{ fieldWithObjectInput(input: {b: ["A", null, "C"], c: "C"}) }')
+    assert result == ast.Document(
+        definitions=[
+            ast.OperationDefinition(
+                operation='query', name=None, variable_definitions=None, directives=[],
+                selection_set=ast.SelectionSet(
+                    selections=[
+                        ast.Field(
+                            alias=None,
+                            name=ast.Name(value=u'fieldWithObjectInput'),
+                            directives=[],
+                            selection_set=None,
+                            arguments=[
+                                ast.Argument(
+                                    name=ast.Name(value=u'input'),
+                                    value=ast.ObjectValue(
+                                        fields=[
+                                            ast.ObjectField(
+                                                name=ast.Name(value=u'b'),
+                                                value=ast.ListValue(
+                                                    values=[
+                                                        ast.StringValue(value=u'A'),
+                                                        ast.NullValue(),
+                                                        ast.StringValue(value=u'C'),
+                                                    ],
+                                                ),
+                                            ),
+                                            ast.ObjectField(
+                                                name=ast.Name(value=u'c'),
+                                                value=ast.StringValue(value=u'C'),
+                                            ),
+                                        ]
+                                    ),
+                                ),
+                            ],
+                        ),
+                    ],
+                ),
+            ),
+        ],
+    )
+
+
+def test_null_as_name():
+    result = parse('{ thingy(null: "stringcheese") }')
+    assert result.definitions[0].selection_set.selections[0].name.value == 'thingy'
+    assert result.definitions[0].selection_set.selections[0].arguments[0].name.value == 'null'
+
+
 def test_parses_multi_byte_characters():
     result = parse(u'''
         # This comment has a \u0A0A multi-byte character.