A broken bootstrap runs no tests and exits 0

[Chemaclass]

Problem

A bootstrap file that fails to load leaves the run with no tests, no summary,
and exit 0 — CI passes having executed nothing.

$ printf 'function broken( {\n' > boot.sh
$ BASHUNIT_BOOTSTRAP=boot.sh bashunit tests/
boot.sh: line 1: syntax error near unexpected token `{'
$ echo $?
0

A bootstrap containing a bare exit 3 is worse still: completely silent, exit 3,
no indication of the cause.

Why nothing caught it

[ -f "$BASHUNIT_BOOTSTRAP" ] && source "$BASHUNIT_BOOTSTRAP" cannot detect
this. source is a POSIX special builtin: a syntax error in the sourced
file, or a bare exit, terminates the shell at that point, so || status=$?
never runs and nothing after the call executes.

The --env/--boot flag path validates its file (#875, same bug class); the
BASHUNIT_BOOTSTRAP env path never did.

Fix

bash -n pre-validation would cost an interpreter fork on every invocation,
which bashunit_coldstart_forks_test.sh caps at 1 — and this repo has a
bootstrap, so all ~258 nested acceptance runs would pay it.

Instead: set a marker before sourcing, clear it after, and let the existing
EXIT trap report a marker that was never cleared. Fork-free, and it catches
both failure modes.

An absent bootstrap stays silent: BASHUNIT_BOOTSTRAP defaults to
tests/bootstrap.sh, which most projects do not have, so failing on it would
break every one of them.

[Chemaclass]

Done in #1180 (merged).

[Chemaclass]

Correction: I stated the wrong mechanism

I wrote that source is a POSIX special builtin and that a syntax error in the
sourced file therefore terminates the shell. That is not what happens.
Measured:

case	result
set +e, syntax error	source returns 1, execution continues
set -e, syntax error	shell exits (status 2)
set +e, bare exit 3	shell exits (status 3)

So the two failure modes have different causes:

• Syntax error — source returns non-zero like any other command. The shell
  only dies because set -e is active at that point in the parse. Nothing to do
  with special builtins.
• Bare exit — that exits the shell whatever set -e says, because it is
  what exit means in a sourced file.

What this does and does not change

The fix stands: a marker plus the EXIT trap is still the design that covers
both, and it is still fork-free. But the alternative I dismissed —
set +e; source …; status=$? — would in fact have caught the syntax-error case;
it just would not have caught a bare exit. My reasoning for rejecting it was
wrong even though the conclusion held.

Recording this because a future reader would otherwise take the special-builtin
claim as fact.