gitbash test fixtures: anchor TMPDIR at the real Windows temp root
git -C /tmp/tmp.XXX/repo fails on gitbash with cannot change to C:\Users\<u>\AppData\Local\Temp\2\tmp\tmp.XXX\repo — note the doubled tmp segment. git's Cygwin path resolver treats /tmp/foo as <Temp2>/tmp/foo, so a path the shell resolves fine ends up looking for a directory the disk doesn't have. Anything that pipes mktemp output into git -C hits it; mine broke ~20 of 60+ tests in one go.
The fix is to set TMPDIR to the real Windows temp root before any mktemp -d call. mktemp then returns C:\Users\<u>\AppData\Local\Temp\2\tmp.XXX (no leading /tmp/) and git's resolver is happy. cygpath -w /tmp gives the right value:
if [[ -n "${MSYSTEM:-}" ]] && command -v cygpath >/dev/null 2>&1; then
export TMPDIR="$(cygpath -w /tmp)"
fi
A few related landmines I tripped over while getting to a green suite — bundle them since you will hit them too:
ln -sfn and readlink round-trip through Cygwin form. Symlink the Windows form C:\Users\...\tmp.X\auth.json and readlink returns /tmp/tmp.X/auth.json. A test that does assert_eq "${primary_home}/auth.json" "$(readlink …)" fails on gitbash even when both point at the same file. A cygpath -u on each side makes them comparable; I added an assert_path_eq helper for this. Don't use cd && pwd -P as the canonicalisation — it fails for target paths that don't yet exist as real directories (the symlink is dangling at assert time).
Windows jq emits CRLF. A pipeline ending in paste -sd, keeps the \r in each token, so expected "3,5,10" got "3\r,5\r,10" is a real failure mode. tr -d '\r' after the jq call fixes it; doing it inside the test's jq wrapper covers most cases.
Windows has no POSIX file mode bits. chmod +x is a no-op, chmod 700 is a no-op, and [[ -x ${path} ]] is always false for a no-extension file. The launch scripts the runtime writes are invoked with bash <path>, so missing exec bit is harmless in production — skip those assertions on MSYSTEM.
bash -x leaks inherited env to the transcript. If the parent shell sources ~/.bashrc.secret (mine does), set -x spews every export OAUTH_TOKEN=… into the output. Diagnostic prints are fine, but never set -x the real test — and redact the log if you did.
These four are the high-leverage fixes; everything else (tmux e2e, setsid/python missing, MINGW64 prompt prefix in pane titles) is one-test-at-a-case and worth a separate pass.