diff --git a/api/src/DateTime.php b/api/src/DateTime.php
index 91b12eba1b..22b636b97a 100644
--- a/api/src/DateTime.php
+++ b/api/src/DateTime.php
@@ -693,35 +693,3 @@ class DateTime extends \DateTime
 	}
 }
 DateTime::init();
-
-/*
-if (isset($_SERVER['SCRIPT_FILENAME']) && $_SERVER['SCRIPT_FILENAME'] == __FILE__)	// some tests
-{
-	// test timestamps/dates before 1970
-	foreach(array('19690811',-3600,'-119322000') as $ts)
-	{
-		try {
-			echo "<p>DateTime::to($ts,'Y-m-d H:i:s')=".DateTime::to($ts,'Y-m-d H:i:s')."</p>\n";
-			$et = new DateTime($ts);
-			echo "<p>DateTime($ts)->format('Y-m-d H:i:s')=".$et->format('Y-m-d H:i:s')."</p>\n";
-			$dt = new DateTime($ts);
-			echo "<p>DateTime($ts)->format('Y-m-d H:i:s')=".$dt->format('Y-m-d H:i:s')."</p>\n";
-		} catch(\Exception $e) {
-			echo "<p><b>Exception</b>: ".$e->getMessage()."</p>\n";
-		}
-	}
-	// user time is UTC
-	echo "<p>user timezone = ".($GLOBALS['egw_info']['user']['preferences']['common']['tz'] = 'UTC').", server timezone = ".date_default_timezone_get()."</p>\n";
-
-	$time = time();
-	echo "<p>time=$time=".date('Y-m-d H:i:s',$time)."(server) =".DateTime::server2user($time,'Y-m-d H:i:s')."(user) =".DateTime::server2user($time,'ts')."(user)=".date('Y-m-d H:i:s',DateTime::server2user($time,'ts'))."</p>\n";
-
-	echo "DateTime::to(array('full' => '20091020', 'hour' => 12, 'minute' => 0))='".DateTime::to(array('full' => '20091020', 'hour' => 12, 'minute' => 0))."'</p>\n";
-
-	$ts = DateTime::to(array('full' => '20091027', 'hour' => 10, 'minute' => 0),'ts');
-	echo "<p>2009-10-27 10h UTC timestamp=$ts --> server time = ".DateTime::user2server($ts,'')." --> user time = ".DateTime::server2user(DateTime::user2server($ts),'')."</p>\n";
-
-	$ts = DateTime::to(array('full' => '20090627', 'hour' => 10, 'minute' => 0),'ts');
-	echo "<p>2009-06-27 10h UTC timestamp=$ts --> server time = ".DateTime::user2server($ts,'')." --> user time = ".DateTime::server2user(DateTime::user2server($ts),'')."</p>\n";
-}
-*/
diff --git a/api/src/test/DateTimeTest.php b/api/src/test/DateTimeTest.php
new file mode 100644
index 0000000000..3b8f9f6db1
--- /dev/null
+++ b/api/src/test/DateTimeTest.php
@@ -0,0 +1,120 @@
+<?php
+
+/**
+ * EGroupware Api: DateTime tests
+ *
+ * @link http://www.stylite.de
+ * @package api
+ * @author Nathan Gray
+ * @copyright (c) 2017 Nathan Gray
+ * @license http://opensource.org/licenses/gpl-license.php GPL - GNU General Public License
+ */
+namespace EGroupware\Api;
+
+require_once realpath(__DIR__.'/../loader/common.php');	// autoloader & check_load_extension
+
+use EGroupware\Api;
+use PHPUnit_Framework_TestCase as TestCase;
+
+/**
+ * Testing the Egroupware extension of DateTime
+ *
+ */
+class DateTimeTest extends TestCase {
+
+	static $usertime;
+
+	/**
+	 * Work in server time, so tests match expectations
+	 */
+	public static function setUpBeforeClass()
+	{
+		parent::setUpBeforeClass();
+
+		static::$usertime = DateTime::$user_timezone;
+
+		// Set user time to server time for consistency
+		DateTime::setUserPrefs(date_default_timezone_get());
+	}
+	public static function tearDownAfterClass()
+	{
+		// Reset
+		DateTime::setUserPrefs(static::$usertime->getName());
+	}
+
+	/**
+	 * Test that dates before 1970 are handled correctly
+	 */
+	public function testBefore1970()
+	{
+		$checklist = array(
+			// Use sub array instead of key/value pair to preserve type
+			// Timestamp         Expected
+			array('19690811',   '1969-08-11 00:00:00'),
+			array(-3600,        '1969-12-31 23:00:00'),
+			array('-119322000', '1966-03-21 23:00:00')
+		);
+		foreach($checklist as $test)
+		{
+			list($ts, $expected) = $test;
+			$this->checkTimestamp($ts, $expected);
+		}
+	}
+
+	/**
+	 * Check timezone conversion is sane - convert back and forth between same
+	 * timezone
+	 */
+	public function testUserTimeEqualsServerTime()
+	{
+		$time = time();
+		$this->assertEquals($time, DateTime::server2user($time, 'ts'));
+		$this->assertEquals(date('Y-m-d H:i:s',$time), DateTime::server2user($time,'Y-m-d H:i:s'));
+
+
+		$this->assertEquals('2009-10-20, 12:00',DateTime::to(array('full' => '20091020', 'hour' => 12, 'minute' => 0)));
+
+		$ts = DateTime::to(array('full' => '20091027', 'hour' => 10, 'minute' => 0),'ts');
+		$this->assertEquals(DateTime::user2server($ts,''), DateTime::server2user(DateTime::user2server($ts),''));
+
+		$ts = DateTime::to(array('full' => '20090627', 'hour' => 10, 'minute' => 0),'ts');
+		$this->assertEquals(DateTime::user2server($ts,''), DateTime::server2user(DateTime::user2server($ts),''));
+	}
+
+	/**
+	 * Test timezone conversion with actual changes
+	 */
+	public function testTimezoneConversion()
+	{
+		// Set server to UTC
+		$server_tz = date_default_timezone_get();
+		date_default_timezone_set('UTC');
+
+		// Set user to Berlin (UTC-1)
+		DateTime::setUserPrefs('Europe/Berlin');
+		$ts = DateTime::to(array('full' => '20091027', 'hour' => 10, 'minute' => 0),'ts');
+		$this->assertEquals('2009-10-27 09:00:00', DateTime::user2server($ts,'Y-m-d H:i:s'));
+
+		// Set user to Cape Verde (UTC+1)
+		DateTime::setUserPrefs('Atlantic/Cape_Verde');
+		$ts = DateTime::to(array('full' => '20091027', 'hour' => 10, 'minute' => 0),'ts');
+		$this->assertEquals('2009-10-27 11:00:00', DateTime::user2server($ts,'Y-m-d H:i:s'));
+
+		date_default_timezone_set($server_tz);
+	}
+
+	/**
+	 * Check that a timestamp matches expectations
+	 *
+	 * @param string|int $ts Something that looks like a time
+	 * @param string $expected Expected time, in Y-m-d H:i:s format
+	 */
+	protected function checkTimestamp($ts, $expected)
+	{
+		$fail_message = "Checking $ts = $expected";
+		$this->assertEquals($expected, DateTime::to($ts,'Y-m-d H:i:s'), $fail_message);
+
+		$dt = new DateTime($ts);
+		$this->assertEquals($expected, $dt->format('Y-m-d H:i:s'), $fail_message);
+	}
+}