test: add regression test for specifiedByURL on __Type

Verifies that specifiedByURL is queryable and returns null for built-in
scalar types and object types, matching the GraphQL Oct 2021 spec.

Author: shkuls

test/expected/resolve_specified_by_url.out

@@ -0,0 +1,30 @@
+begin;
+    comment on schema public is e'@graphql({"inflect_names": true, "introspection": true})';
+    -- specifiedByURL should be queryable and return null for built-in scalars
+    select graphql.resolve(
+        query:='{ __type(name: "Boolean") { specifiedByURL } }'
+    );
+                              resolve
+------------------------------------------------------------------
+ {"data": {"__type": {"specifiedByURL": null}}}
+(1 row)
+
+    -- specifiedByURL should also work alongside other fields
+    select graphql.resolve(
+        query:='{ __type(name: "String") { name kind specifiedByURL } }'
+    );
+                                            resolve
+----------------------------------------------------------------------------------------------
+ {"data": {"__type": {"kind": "SCALAR", "name": "String", "specifiedByURL": null}}}
+(1 row)
+
+    -- specifiedByURL on a non-scalar type (e.g. OBJECT) should also return null
+    select graphql.resolve(
+        query:='{ __type(name: "Query") { name kind specifiedByURL } }'
+    );
+                                           resolve
+---------------------------------------------------------------------------------------------
+ {"data": {"__type": {"kind": "OBJECT", "name": "Query", "specifiedByURL": null}}}
+(1 row)
+
+rollback;

test/sql/resolve_specified_by_url.sql

@@ -0,0 +1,19 @@
+begin;
+    comment on schema public is e'@graphql({"inflect_names": true, "introspection": true})';
+
+    -- specifiedByURL should be queryable and return null for built-in scalars
+    select graphql.resolve(
+        query:='{ __type(name: "Boolean") { specifiedByURL } }'
+    );
+
+    -- specifiedByURL should also work alongside other fields
+    select graphql.resolve(
+        query:='{ __type(name: "String") { name kind specifiedByURL } }'
+    );
+
+    -- specifiedByURL on a non-scalar type (e.g. OBJECT) should also return null
+    select graphql.resolve(
+        query:='{ __type(name: "Query") { name kind specifiedByURL } }'
+    );
+
+rollback;