Initially BaseWicketTester#startComponent(Component) has been introduced to test a component without attaching it to a page (this is what its Javadoc states).
First it appeared that the tested component is not initialized (fixed with https://issues.apache.org/jira/browse/WICKET-4792).
Then https://issues.apache.org/jira/browse/WICKET-4976 - the request cycle and the component itself are not detached at the end.
And now a colleague of mine reported me that since
WICKET-4976 a test is failing in our app because our custom IRequestCycleListener#onEndRequest() is called but #onBeginRequest() hasn't been called before that. I remember Hielke from Topicus also had this problem for Wiquery 6.6.0.
BaseWicketTester#startComponent(Component) becomes more and more the same as #startComponentInPage(Component) so it will be deprecated in 6.x series and fully removed with Wicket 7.0.0