I created a team called 'Blue' and assigned 8 silverfishes to the team (also tried with 1) and did both /testfor @e[team=Blue] and /say @e[team=Blue] and got no comparator output from the /testfor, and "That player cannot be found" for /say command.
All the commands I used:
1) /scoreboard teams add Blue
2) /scoreboard teams join Blue @e[type=Silverfish]
3) /testfor @e[team=Blue]
4) /say @e[team=Blue]
Linked issues
Comments 3
Confirmed for 14w26b
This really don't feel like duplicate of MC-46956, which is about the "teams options" tags like FriendlyFire and SeeFriendlyInvisibles not working on entities.
THIS bug report is about a particular selector tag (team=) not working on entities. Example:
/testfor @e[team=Blue]
michael
Maybe this bug(MC-58808) and the one you reported have the same source