ant target "compile-tests" doesn't include "${main.classes.dir}" in classpath ..
<javac srcdir="{test.src.dir}" destdir="
{test.classes.dir}"
classpath="**{main.classes.dir}:**
{lib.dir}/${hipparchus.core.jar}: .
. . .
(from redmine: issue id 246, created on 2016-06-29, closed on 2017-07-27)