JSON.serialize is mucking with my datetime objects. How do I fix this?

Question

I feel that the following assertion should be true, but it is not:

DateTime testDate = DateTime.now();
System.assertEquals('"' + testDate.format('yyyy-MM-dd\'T\'hh:mm:ss.SSS\'Z\'' + '"'), JSON.serialize(testDate));

I get the following error:

16:38:28.966 (2966802000)|FATAL_ERROR|System.AssertException: Assertion Failed: Expected: "2014-04-03T04:38:27.988Z", Actual: "2014-04-03T20:38:27.988Z"

Update: when using formatGMT I still get the error:

DateTime testDate = DateTime.now();
System.assertEquals('"' + testDate.formatGMT('yyyy-MM-dd\'T\'hh:mm:ss.SSS\'Z\'' + '"'), JSON.serialize(testDate));

16:51:32.228 (2228010000)|FATAL_ERROR|System.AssertException: Assertion Failed: Expected: "2014-04-03T08:51:31.274Z", Actual: "2014-04-03T20:51:31.274Z"

Answer 1

I think the time wasn't in the correct format

DateTime testDate = DateTime.now(); System.assertEquals('"' + testDate.formatGMT('yyyy-MM-dd\'T\'HH:mm:ss.SSS\'Z\'' + '"'), JSON.serialize(testDate));

Answer 2

The DateTime.format() method converts the value to the time zone of the user who is running the test. The serializer is displaying the value as GMT.

A simple solution would be to use the DateTime.formatGMT() method in your test.

DateTime testDate = DateTime.now();
System.assertEquals('"' + testDate.formatGMT('yyyy-MM-dd\'T\'hh:mm:ss.SSS\'Z\'' + '"'), JSON.serialize(testDate));

Update: (The problem is in the format string as noted by @melmoussaoui - 'HH' vs 'hh')

DateTime testDate = DateTime.now();
String expectedValue = '"' + testDate.formatGMT('yyyy-MM-dd\'T\'HH:mm:ss.SSS\'Z\'' + '"');
String actualValue = JSON.serialize(testDate);
system.debug('Expected: ' + expectedValue);
system.debug('Actual:   ' + actualValue);
System.assertEquals(expectedValue, actualValue);

Debug output:

14:12:04:046 USER_DEBUG [4]|DEBUG|Expected: "2014-04-03T21:12:04.853Z"
14:12:04:046 USER_DEBUG [5]|DEBUG|Actual:   "2014-04-03T21:12:04.853Z"

Salesforce DateTime methods