Add simple test for instanceOf. (#1370)

Author: IvanGoncharov

src/jsutils/__tests__/instanceOf-test.js

@@ -0,0 +1,28 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import { expect } from 'chai';
+import { describe, it } from 'mocha';
+import instanceOf from '../instanceOf';
+
+describe('instanceOf', () => {
+  it('fails with descriptive error message', () => {
+    function getFoo() {
+      class Foo {}
+      return Foo;
+    }
+    const Foo1 = getFoo();
+    const Foo2 = getFoo();
+
+    expect(() => instanceOf(new Foo1(), Foo2)).to.throw(
+      /^Cannot use Foo "\[object Object\]" from another module or realm./m,
+    );
+    expect(() => instanceOf(new Foo2(), Foo1)).to.throw(
+      /^Cannot use Foo "\[object Object\]" from another module or realm./m,
+    );
+  });
+});