Be strict about request counting in tests

The angular $httpBackend mocking service supports two primary means of
usage:

   .expect(...).respond(...)

and

   .when(...).respond(...)

The latter pattern allows a single handler to respond to multiple
requests, in any order. The latter is precise -- one .expect() must be
matched by one request, in the correct order.

This commit changes the tests for the "features" service to use this
more precise form of testing.

h/static/scripts/test/features-test.js

@@ -8,7 +8,6 @@ sinon.assert.expose(assert, {prefix: null});
 
 describe('h:features', function () {
   var $httpBackend;
-  var httpHandler;
   var features;
   var sandbox;
 
@@ -32,9 +31,6 @@ describe('h:features', function () {
   beforeEach(mock.inject(function ($injector) {
     $httpBackend = $injector.get('$httpBackend');
     features = $injector.get('features');
-
-    httpHandler = $httpBackend.when('GET', 'http://foo.com/app/features');
-    httpHandler.respond(200, {foo: true, bar: false});
   }));
 
   afterEach(function () {
@@ -43,25 +39,32 @@ describe('h:features', function () {
     sandbox.restore();
   });
 
+  function defaultHandler() {
+    var handler = $httpBackend.expect('GET', 'http://foo.com/app/features');
+    handler.respond(200, {foo: true, bar: false});
+    return handler;
+  }
+
   it('fetch should retrieve features data', function () {
-    $httpBackend.expect('GET', 'http://foo.com/app/features');
+    defaultHandler();
     features.fetch();
     $httpBackend.flush();
   });
 
   it('fetch should not explode for errors fetching features data', function () {
-    httpHandler.respond(500, "ASPLODE!");
+    defaultHandler().respond(500, "ASPLODE!");
     features.fetch();
     $httpBackend.flush();
   });
 
   it('flagEnabled should retrieve features data', function () {
-    $httpBackend.expect('GET', 'http://foo.com/app/features');
+    defaultHandler();
     features.flagEnabled('foo');
     $httpBackend.flush();
   });
 
   it('flagEnabled should return false initially', function () {
+    defaultHandler();
     var result = features.flagEnabled('foo');
     $httpBackend.flush();
 
@@ -69,6 +72,7 @@ describe('h:features', function () {
   });
 
   it('flagEnabled should return flag values when data is loaded', function () {
+    defaultHandler();
     features.fetch();
     $httpBackend.flush();
 
@@ -80,6 +84,7 @@ describe('h:features', function () {
   });
 
   it('flagEnabled should return false for unknown flags', function () {
+    defaultHandler();
     features.fetch();
     $httpBackend.flush();
 
@@ -90,13 +95,13 @@ describe('h:features', function () {
   it('flagEnabled should trigger a new fetch after cache expiry', function () {
     var clock = sandbox.useFakeTimers();
 
-    $httpBackend.expect('GET', 'http://foo.com/app/features');
+    defaultHandler();
     features.flagEnabled('foo');
     $httpBackend.flush();
 
     clock.tick(301 * 1000);
 
-    $httpBackend.expect('GET', 'http://foo.com/app/features');
+    defaultHandler();
     features.flagEnabled('foo');
     $httpBackend.flush();
   });