diff --git a/platform/framework/test/register/ExtensionRegistrarSpec.js b/platform/framework/test/register/ExtensionRegistrarSpec.js
index cd57ded64e..f6130b4030 100644
--- a/platform/framework/test/register/ExtensionRegistrarSpec.js
+++ b/platform/framework/test/register/ExtensionRegistrarSpec.js
@@ -4,11 +4,65 @@
  * ExtensionRegistrarSpec. Created by vwoeltje on 11/6/14.
  */
 define(
-    [],
-    function () {
+    ["../../src/register/ExtensionRegistrar"],
+    function (ExtensionRegistrar) {
         "use strict";
 
-        describe("", function () {
+        describe("The extension registrar", function () {
+            var mockApp,
+                mockLog,
+                customRegistrars,
+                registrar;
+
+            beforeEach(function () {
+                mockApp = jasmine.createSpyObj("app", ["factory"]);
+                mockLog = jasmine.createSpyObj("$log", ["error", "warn", "debug", "info"]);
+                customRegistrars = {};
+                registrar = new ExtensionRegistrar(mockApp, customRegistrars, mockLog);
+            });
+
+            it("registers extensions using the factory", function () {
+                registrar.registerExtensions({ things: [ {} ] });
+                expect(mockApp.factory).toHaveBeenCalled();
+            });
+
+            it("registers extensions with square brackets, as arrays", function () {
+                var callbacks = {};
+                mockApp.factory.andCallFake(function (name, value) {
+                    callbacks[name] = value[value.length - 1];
+                });
+                registrar.registerExtensions({ things: [ {} ] });
+                expect(callbacks["things[]"]).toBeDefined();
+
+                // Verify dependency echo behavior
+                expect(callbacks["things[]"]("a", "b", "c")).toEqual(["a", "b", "c"]);
+            });
+
+            it("warns if multiple registrations are made for the same category of extension", function () {
+                registrar.registerExtensions({ things: [ {} ] });
+                expect(mockLog.warn).not.toHaveBeenCalled();
+                registrar.registerExtensions({ things: [ {} ] });
+                expect(mockLog.warn).toHaveBeenCalled();
+            });
+
+            it("registers empty extension categories when they are needed", function () {
+                var lengths = {};
+                mockApp.factory.andCallFake(function (name, value) {
+                    lengths[name] = value.length;
+                });
+                // Nobody has registered tests[], but it looks like an extension dependency,
+                // so register it as an empty array.
+                registrar.registerExtensions({ things: [ { depends: [ "tests[]", "other" ] } ] });
+                expect(lengths["tests[]"]).toEqual(1);
+                expect(lengths.other).toBeUndefined();
+            });
+
+            it("invokes custom registrars (not app.factory) when available", function () {
+                customRegistrars.things = jasmine.createSpy("things");
+                registrar.registerExtensions({ things: [ {} ] });
+                expect(mockApp.factory).not.toHaveBeenCalled();
+                expect(customRegistrars.things).toHaveBeenCalled();
+            });
 
         });
     }