Question re testing configuration

Hi all,

I'm a new developer trying to get my feet wet and I'm running into an issue with the tests that I can't figure out at this point.

I *know* that the changes I'm working on are causing the tests to fail, but I can't figure out how to induce the failure manually (so that I can throw gdb at the problem).

Specifically I'm seeing t5000-tar-tree.sh fail (as a result of adding extra diff_populate_filespec() calls before the estimate_similarity() loop in diffcore_rename()) on #52 "set up repository with huge blob" and #55 "set up repository with far-future commit".

If I run the commands fed into test_expect_success in t5000, though (in an empty repo initialized with git init), making sure to use the binary compiled with the breaking changes, the command doesn't fail, so I'm clearly missing something in the testing environment setup when I try to manually reproduce it.

Can someone point me in the right direction? I've spent some time now going through t/test-lib.sh and I haven't figured it out yet.

Thanks, Sam