fixup! simplify and improve test info

Author: Narretz

src/ng/directive/input.js

@@ -1443,10 +1443,11 @@ function createDateInputType(type, regexp, parseDate, format) {
         // Note: We cannot read ctrl.$modelValue, as there might be a different
         // parser/formatter in the processing chain so that the model
         // contains some different data format!
-        if (timezone && previousTimezone && previousTimezone !== timezone) {
-          // If the timezone has changed, adjust the previousDate to the default timzeone
+
+        if (previousTimezone && previousTimezone !== timezone) {
+          // If the timezone has changed, adjust the previousDate to the default timezone
           // so that the new date is converted with the correct timezone offset
-          previousDate = addDateMinutes(previousDate, timezoneToOffset(previousTimezone, 0));
+          previousDate = addDateMinutes(previousDate, timezoneToOffset(previousTimezone));
         }
 
         var parsedDate = parseDate(value, previousDate);

test/ng/directive/inputSpec.js

@@ -980,15 +980,23 @@ describe('input', function() {
     it('should be possible to override the timezone', function() {
       var inputElm = helper.compileInput('<input type="week" ng-model="value" ng-model-options="{timezone: \'UTC\'}" />');
 
-      helper.changeInputValueTo('2013-W03');
-      expect(+$rootScope.value).toBe(Date.UTC(2013, 0, 17));
+      // January 19 2013 is a Saturday
+      $rootScope.$apply(function() {
+        $rootScope.value = new Date(Date.UTC(2013, 0, 19));
+      });
+
+      expect(inputElm.val()).toBe('2013-W03');
 
-      inputElm.controller('ngModel').$overrideModelOptions({timezone: '+5000'});
+      inputElm.controller('ngModel').$overrideModelOptions({timezone: '+2400'});
 
+      // To check that the timezone overwrite works, apply an offset of +24 hours.
+      // Since January 19 is a Saturday, +24 will turn the formatted Date into January 20 - Sunday -
+      // which is in calendar week 4 instead of 3.
       $rootScope.$apply(function() {
-        // the 17. with an offset of +5000 moves the date into next week
-        $rootScope.value = new Date(Date.UTC(2013, 0, 18));
+        $rootScope.value = new Date(Date.UTC(2013, 0, 19));
       });
+
+      // Verifying that the displayed week is week 4 confirms that overriding the timezone worked
       expect(inputElm.val()).toBe('2013-W04');
     });
 
@@ -1997,30 +2005,34 @@ describe('input', function() {
       dealoc(formElm);
     });
 
-    it('should not reuse the hour part of a previous date object after changing the timezone', function() {
+    it('should not reuse the hours part of a previous date object after changing the timezone', function() {
       var inputElm = helper.compileInput('<input type="date" ng-model="value" ng-model-options="{timezone: \'UTC\'}" />');
 
       helper.changeInputValueTo('2000-01-01');
+      // The Date parser sets the hours part of the Date to 0 (00:00) (UTC)
       expect(+$rootScope.value).toBe(Date.UTC(2000, 0, 1, 0));
 
       // Change the timezone offset so that the display date is a day earlier
       // This does not change the model, but our implementation
       // internally caches a Date object with this offset
-      // and re-uses it if part of the date changes
+      // and re-uses it if part of the Date changes.
+      // See https://github.com/angular/angular.js/commit/1a1ef62903c8fdf4ceb81277d966a8eff67f0a96
       inputElm.controller('ngModel').$overrideModelOptions({timezone: '-0500'});
       $rootScope.$apply(function() {
         $rootScope.value = new Date(Date.UTC(2000, 0, 1, 0));
       });
       expect(inputElm.val()).toBe('1999-12-31');
 
-      // Emptying the input should clear the cached date object
-      helper.changeInputValueTo('');
-
+      // At this point, the cached Date has its hours set to to 19 (00:00 - 05:00 = 19:00)
       inputElm.controller('ngModel').$overrideModelOptions({timezone: 'UTC'});
+
+      // When changing the timezone back to UTC, the hours part of the Date should be set to
+      // the default 0 (UTC) and not use the modified value of the cached Date object.
       helper.changeInputValueTo('2000-01-01');
       expect(+$rootScope.value).toBe(Date.UTC(2000, 0, 1, 0));
     });
 
+
     describe('min', function() {
 
       it('should invalidate', function() {