to test the apex classes, execute the following code (create a CustomLabel, update a CustomLabel , delete the customLabel created) :
System.debug(ToolingApiUtil.execSoql('select Id,Value,Name from ExternalString',false));
ToolingUtilDemo.createCustomLabel('test2','test2','test2');
System.debug(ToolingApiUtil.execSoql('select Id,Value,Name from ExternalString',false));
ToolingUtilDemo.updateCustomLabelValue('test3','test2');
System.debug(ToolingApiUtil.execSoql('select Id,Value,Name from ExternalString',false));
ToolingUtilDemo.deleteCustomLabelValue('test2');
System.debug(ToolingApiUtil.execSoql('select Id,Value,Name from ExternalString',false));