Testament singles?

"The single" can refer to whatever track the band or label is using to promote a release. They might press discs specifically for that purpose but it's pretty common to just pick a specific track off a full length. In Testament's case, they were on a major so things tended to be done a bit more traditonally/costly so the single track or three with bsides varieties did exist.
As for commercially available ones... couldn't say.