There are some bugs related to cookie handling in BaseWicketTester.
Problem 1) a cookie set in the request should not be in the response unless manually set by the server code
Problem 2) wicket tester sends the original cookie instance to the server. If the server code manipulates the cookie anyhow (e.g. change its value) but do not send it back explicitly in the response then the original cookie in WicketTester (the request cookie) is updated while it shouldn't be.
A possible solutions for these problems can be found at: