Error logging for new interface type semantics

src/type/__tests__/schema-test.js

@@ -0,0 +1,61 @@
+/**
+ *  Copyright (c) 2015, Facebook, Inc.
+ *  All rights reserved.
+ *
+ *  This source code is licensed under the BSD-style license found in the
+ *  LICENSE file in the root directory of this source tree. An additional grant
+ *  of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+import {
+  GraphQLSchema,
+  GraphQLInterfaceType,
+  GraphQLObjectType,
+  GraphQLString
+} from '../';
+
+import { describe, it } from 'mocha';
+import { expect } from 'chai';
+
+const InterfaceType = new GraphQLInterfaceType({
+  name: 'Interface',
+  fields: { fieldName: { type: GraphQLString } },
+  resolveType() {
+    return ImplementingType;
+  }
+});
+
+const ImplementingType = new GraphQLObjectType({
+  name: 'Object',
+  interfaces: [ InterfaceType ],
+  fields: { fieldName: { type: GraphQLString, resolve: () => '' }}
+});
+
+const Schema = new GraphQLSchema({
+  query: new GraphQLObjectType({
+    name: 'Query',
+    fields: {
+      getObject: {
+        type: InterfaceType,
+        resolve() {
+          return {};
+        }
+      }
+    }
+  })
+});
+
+describe('Type System: Schema', () => {
+  describe('Getting possible types', () => {
+    it('throws human-reable error if schema.types is not defined', () => {
+      const checkPossible = () => {
+        return Schema.isPossibleType(InterfaceType, ImplementingType);
+      };
+      expect(checkPossible).to.throw(
+        'Could not find possible implementing types for Interface in schema. ' +
+        'Check that schema.types is defined and is an array ofall possible ' +
+        'types in the schema.'
+      );
+    });
+  });
+});

src/type/schema.js

@@ -183,8 +183,15 @@ export class GraphQLSchema {
     }
 
     if (!possibleTypeMap[abstractType.name]) {
+      const possibleTypes = this.getPossibleTypes(abstractType);
+      invariant(
+        Array.isArray(possibleTypes),
+        `Could not find possible implementing types for ${abstractType} in ` +
+        'schema. Check that schema.types is defined and is an array of' +
+        'all possible types in the schema.'
+      );
       possibleTypeMap[abstractType.name] =
-        this.getPossibleTypes(abstractType).reduce(
+        possibleTypes.reduce(
           (map, type) => ((map[type.name] = true), map),
           Object.create(null)
         );