test: Adds type reference resolution tests

Author: NeedleInAJayStack

Tests/GraphQLTests/TypeTests/GraphQLSchemaTests.swift

@@ -157,4 +157,56 @@ class GraphQLSchemaTests: XCTestCase {
             )
         }
     }
+
+    func testAssertSchemaCircularReference() throws {
+        let object1 = try GraphQLObjectType(
+            name: "Object1",
+            fields: [
+                "object2": GraphQLField(
+                    type: GraphQLTypeReference("Object2")
+                ),
+            ]
+        )
+        let object2 = try GraphQLObjectType(
+            name: "Object2",
+            fields: [
+                "object1": GraphQLField(
+                    type: GraphQLTypeReference("Object1")
+                ),
+            ]
+        )
+        let query = try GraphQLObjectType(
+            name: "Query",
+            fields: [
+                "object1": GraphQLField(type: GraphQLTypeReference("Object1")),
+                "object2": GraphQLField(type: GraphQLTypeReference("Object2")),
+            ]
+        )
+
+        let schema = try GraphQLSchema(query: query, types: [object1, object2])
+        for (_, graphQLNamedType) in schema.typeMap {
+            XCTAssertFalse(graphQLNamedType is GraphQLTypeReference)
+        }
+    }
+
+    func testAssertSchemaFailsWhenObjectNotDefined() throws {
+        let object1 = try GraphQLObjectType(
+            name: "Object1",
+            fields: [
+                "object2": GraphQLField(
+                    type: GraphQLTypeReference("Object2")
+                ),
+            ]
+        )
+        let query = try GraphQLObjectType(
+            name: "Query",
+            fields: [
+                "object1": GraphQLField(type: GraphQLTypeReference("Object1")),
+            ]
+        )
+
+        XCTAssertThrowsError(
+            _ = try GraphQLSchema(query: query, types: [object1])
+        )
+    }
 }