When running "make tests" the following tests fail with the error:

Test file error: can't find package tcltests
    while executing
"package require tcltests"
    (in namespace eval "::tcl::test::io" script line 15)
    invoked from within
"namespace eval ::tcl::test::io {
    namespace import ::tcltest::*

After a bit if fossil bisecting, I traced the problem to the following checkin:

basra:unix seandeelywoods$ fossil bisect good
bisect complete
  1 BAD     2018-09-29 20:39:10 6cedb893996a6ba9
  3 BAD     2018-09-24 16:19:17 dad7a5e5dc8284f5
  4 BAD     2018-09-22 10:09:23 645fb65227bbf857
  5 BAD     2018-09-13 20:30:20 0db5ab91bb811088
  6 BAD     2018-09-12 19:30:00 b74093feee50eb76
  7 GOOD    2018-09-07 22:23:00 4ccc3b6902e81691 CURRENT
  2 GOOD    2018-09-07 12:11:01 e891020c32f0a710

That checkin marked the introduction of Tip 430 to the core. Initially it was thought that trunk was immune to the bug, but it turned out the tests only failed if make install was performed at some point using that tcl version.

This issue was ultimately tracked down to a mistake in the tip430 implementation. In tclInterp.c around line 400, the new code to use zipfs to locate tcl_library was being called before the check to see if TCL_LIBRARY had been set in the environment. The zipfs code was moved to after he env() check. in checkin [3581eefbc3]. Which has eliminated the issue.

The problems in this ticket are fixed in checkin [3581eefbc3].