It has been provided by testtools to ease migration from python 2, but was deprecated in 2.7.2[1] and will be removed in 2.8.0[2]. [1] https://github.com/testing-cabal/testtools/commit/e0d56b7ce65ae5b3d [2] https://github.com/testing-cabal/testtools/commit/f01e86084e6a858d1 Change-Id: I8b68212a88553aff5c3b4182c246b3c0f7365cf6