No way to replace Set-Cookie header via MockHttpServletResponse #23512
Description
I am trying to test a servlet filter passing it an instance of MockHttpServletResponse.
The filter attempts to overwrite existing Set-Cookie headers with a new Set-Cookie header calling the response.setHeader method. This works on Jetty and Tomcat, however it does not work on the MockHttpServletResponse - leading my tests to fail.
The MockHttpServletResponse actually adds a new Set-Cookie header when using the setHeader method - possibly in contradiction to the HttpServletResponse interface contract.
From inspection, it appears the setSpecialHeader method contains a treatment of Set-Cookie which other container implementations do not have. In other containers e.g. Jetty or Tomcat, the set of special headers is limited to Content-Type or Content-Length. In the MockHttpServletResponse, the set of special headers also contains Language and Set-Cookie (see line 589) - which then leads to the Set-Cookie header to be added, rather than replaced.
This difference means I can not test the behavior of my filter in a way consistent with how it will be deployed.