Braking action "good" only means that the friction coefficient (mu) is better that 0.40.
Depending on where you look, you will find different typical friction coefficients between rubber and concrete: Wikipedia says 1.00 (dry) and 0.30 (wet), while
this site quotes various sources between 0.60-0.85 (dry) and 0.25-0.75 (wet).
From my experience, grooved wet runways, ie uncontaminated but not dry, will have braking action good, that is to say better than 0.40. However, the fact that braking action is reported to be good, does not indicate that the runway is dry. The only way to know for sure before you get there, is to obtain information on the runway state. This is sometimes given by ATC automatically, by request, via ATIS or via SNOWTAM or MOTNE codes.