There is a lot of confusion about braking action amongst pilots and others. There are activities underway that will hopefully solve these problems (TALPA ARC initiative). If you maintain a runway to the friction levels cited by ICAO, a wet runway will perform like braking action good as defined in the QRH. I know that AMS does runway maintenance friction tests. Braking action poor typically occurs on wet melting ice runways and during special cases like revered rubber hydroplaning. Under normal hydroplaning you will have very low friction levels only at the higher speeds above the full dynamic hydroplaning speed.
Check out the following presentation:
http://www.pilots.or.kr/upfile/aip/9AAAA_StoppingonSlipperyRwys2.ppt