public void setUpEmptySystemProperty(final String propertyName) {
setUpSystemProperty(propertyName, null);
}
public void setUpSystemTime(TimeSource source) {
final TimeSource systemTimeSource = SystemTime.getSource();
SystemTime.set(source);
registerCleanupAction(new CleanupAction() {
public void perform() throws Exception {
SystemTime.set(systemTimeSource);
}