Make user aware of server side errors when saving subscription products and unit test products_panel_controller

spec/javascripts/unit/admin/subscriptions/controllers/products_panel_controller_spec.js.coffee

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+describe "ProductsPanelController", ->
+  scope = null
+  StatusMessage = null
+  subscription = { shop_id: 1 }
+
+  beforeEach ->
+    module('admin.subscriptions')
+    inject ($controller, $rootScope, _StatusMessage_) ->
+      scope = $rootScope
+      scope.object =  subscription
+      StatusMessage = _StatusMessage_
+      $controller 'ProductsPanelController', {$scope: scope, StatusMessage: _StatusMessage_}
+
+  describe "saving subscription", ->
+    update_promise_resolve = null
+    update_promise_reject = null
+    update_promise = null
+
+    beforeEach ->
+      update_promise = new Promise (resolve, reject) ->
+        update_promise_resolve = resolve
+        update_promise_reject = reject
+      subscription.update = jasmine.createSpy('update').and.returnValue(update_promise)
+      StatusMessage.display = jasmine.createSpy('display')
+
+    it "updates subscription and updates status message while in progress and on success", ->
+      scope.save()
+
+      expect(subscription.update).toHaveBeenCalled()
+      expect(StatusMessage.display).toHaveBeenCalledWith('progress', 'Saving...')
+      expect(scope.saving).toEqual(true)
+
+      update_promise.then ->
+        expect(StatusMessage.display.calls.all()[1].args).toEqual(['success', 'Changes saved.'])
+        expect(scope.saving).toEqual(false)
+      update_promise_resolve()
+
+    it "updates status message on errors", ->
+      scope.save()
+
+      update_promise.catch ->
+        expect(StatusMessage.display.calls.all()[1].args).toEqual(['failure', 'Error saving subscription'])
+        expect(scope.saving).toEqual(false)
+      update_promise_reject("error")