Update to 00_Unit_Testing

Additional section with instructions on running tests using in memory SQLite,

docs/en/02_Developer_Guides/06_Testing/00_Unit_Testing.md

@@ -116,6 +116,46 @@ limited than using `phpunit` directly, particularly around formatting test outpu
 	sake dev/tests/all SkipTests=MySkippedTest
 	# Skip some tests
 
+## Making Tests Run Fast
+A major impedement to testing is that by default tests are extremely slow to run.  There are two things that can be done to speed them up:
+
+### Disable xDebug
+Unless executing a coverage report there is no need to have xDebug enabled.
+
+    :::bash
+    # Disable xdebug
+    sudo php5dismod xdebug
+    
+    # Run tests
+    phpunit framework/tests/
+    
+    # Enable xdebug
+    sudo php5enmod xdebug
+    
+### Use SQLite In Memory
+SQLIte can be configured to fun in memory as opposed to disk and this makes testing an order of magnitude faster.  To effect this change add the following to mysite/_config.php - this enables an optional flag to switch between MySQL and SQLite.  Note also that the package silverstripe/sqlite3 will need installed, version will vary depending on which version of SilverStripe is being tested.
+
+    :::php
+    if(Director::isDev()) {
+    	if(isset($_GET['db']) && ($db = $_GET['db'])) {
+        	global $databaseConfig;
+        	if($db == 'sqlite3') {
+        		$databaseConfig['type'] = 'SQLite3Database';
+        		$databaseConfig['path'] = ':memory:';
+        	}
+    	}
+	}
+
+To use SQLite append '' db=sqlite3 after the phpunit command.
+
+    :::bash
+    phpunit framework/tests '' db=sqlite3
+    
+### Speed Comparison
+Testing against a medium sized module with 93 tests:
+* SQLite - 16.15s
+* MySQL - 314s
+This means using SQLite will run tests over 20 times faster.
 
 ## Test Databases and Fixtures