I believe the term comes from IBM history... maybe from the s/360 project.  A separate team was used to test the software... and to build a little team spirit, they dressed in black and developed an extremely aggressive testing process. 

Their job wasn't to merely test the software, their job was to break it!! They became quite happy with their work... while developers became quite unhappy with them.  It is said that a BlackTeam tester would shriek with joy when a bug that broke the software was discovered.

A chapter in DeMarco and Lister's classic book Peopleware celebrated the Black Team as an example of how effective a gelled team can be at perpetuating its culture even when all the original members of the team have long since moved on.
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CategoryTesting