polish(OverlappingFieldsCanMerge): add tests documenting existing behavior

Replicates graphql/graphql-js@cbecc6e

Author: Cito

tests/validation/test_overlapping_fields_can_be_merged.py

@@ -411,6 +411,68 @@ def deep_conflict_with_multiple_issues():
             ],
         )
 
+    def does_not_compare_subfields_of_incompatible_parent_calls():
+        assert_errors(
+            """
+            fragment incompatibleParents on Dog {
+              parent: mother {
+                value: name
+              }
+              parent: father {
+                value: mother { name }
+              }
+            }
+            """,
+            [
+                {
+                    "message": "Fields 'parent' conflict because"
+                    " 'mother' and 'father' are different fields."
+                    " Use different aliases on the fields"
+                    " to fetch both if this was intentional.",
+                    "locations": [(3, 15), (6, 15)],
+                }
+            ],
+        )
+
+    def still_compares_subfields_of_each_compatible_parent_call_group():
+        assert_errors(
+            """
+            fragment mixedParents on Dog {
+              parent: mother {
+                value: name
+              }
+              parent: mother {
+                value: mother { name }
+              }
+              parent: father { name }
+            }
+            """,
+            [
+                {
+                    "message": "Fields 'parent' conflict because"
+                    " subfields 'value' conflict because"
+                    " 'name' and 'mother' are different fields."
+                    " Use different aliases on the fields"
+                    " to fetch both if this was intentional.",
+                    "locations": [(3, 15), (4, 17), (6, 15), (7, 17)],
+                },
+                {
+                    "message": "Fields 'parent' conflict because"
+                    " 'mother' and 'father' are different fields."
+                    " Use different aliases on the fields"
+                    " to fetch both if this was intentional.",
+                    "locations": [(3, 15), (9, 15)],
+                },
+                {
+                    "message": "Fields 'parent' conflict because"
+                    " 'mother' and 'father' are different fields."
+                    " Use different aliases on the fields"
+                    " to fetch both if this was intentional.",
+                    "locations": [(6, 15), (9, 15)],
+                },
+            ],
+        )
+
     def very_deep_conflict():
         assert_errors(
             """
@@ -523,10 +585,10 @@ def reports_deep_conflict_in_nested_fragments():
             """
             {
               field {
-                ...F
+                ...I
               },
               field {
-                ...I
+                ...F
               }
             }
             fragment F on T {
@@ -547,19 +609,19 @@ def reports_deep_conflict_in_nested_fragments():
             [
                 {
                     "message": "Fields 'field' conflict"
-                    " because subfields 'x' conflict"
-                    " because 'a' and 'b' are different fields"
-                    " and subfields 'y' conflict"
-                    " because 'c' and 'd' are different fields."
+                    " because subfields 'y' conflict"
+                    " because 'd' and 'c' are different fields"
+                    " and subfields 'x' conflict"
+                    " because 'b' and 'a' are different fields."
                     " Use different aliases on the fields"
                     " to fetch both if this was intentional.",
                     "locations": [
                         (3, 15),
-                        (11, 15),
-                        (15, 15),
-                        (6, 15),
-                        (22, 15),
                         (18, 15),
+                        (22, 15),
+                        (6, 15),
+                        (15, 15),
+                        (11, 15),
                     ],
                     "path": None,
                 }
@@ -621,6 +683,7 @@ def describe_return_types_must_be_unambiguous():
               scalar: String
               deepBox: StringBox
               unrelatedField: String
+              listNode: [Node]
               listStringBox: [StringBox]
               stringBox: StringBox
               intBox: IntBox
@@ -630,6 +693,7 @@ def describe_return_types_must_be_unambiguous():
               scalar: Int
               deepBox: IntBox
               unrelatedField: String
+              node: Node
               listStringBox: [StringBox]
               stringBox: StringBox
               intBox: IntBox
@@ -754,6 +818,32 @@ def disallows_differing_return_types_despite_no_overlap():
                 schema,
             )
 
+        def does_not_compare_subfields_after_a_response_type_conflict():
+            assert_errors(
+                """
+                {
+                  someBox {
+                    ... on StringBox {
+                      parent: listNode { value: name }
+                    }
+                    ... on IntBox {
+                      parent: node { value: id }
+                    }
+                  }
+                }
+                """,
+                [
+                    {
+                        "message": "Fields 'parent' conflict because"
+                        " they return conflicting types '[Node]' and 'Node'."
+                        " Use different aliases on the fields"
+                        " to fetch both if this was intentional.",
+                        "locations": [(5, 23), (8, 23)],
+                    }
+                ],
+                schema,
+            )
+
         def reports_correctly_when_a_non_exclusive_follows_an_exclusive():
             assert_errors(
                 """