This class is in the src/tests/junit/org/apache/tools/ant directory of Ant source package. It appears we don't package it anywhere, but it is needed to build tests like those of Ivy-2.0.0. So we should package it somewhere, maybe ant-test package? Or in junit with an ant USE flag?
Added as ant-testutil-1.8.0 - it was a jar that we previously did not build.