The bootstrap error says 'cannot read' for three different causes

[Chemaclass]

Problem

-e/--env/--boot reports the same message whatever went wrong:

$ bashunit --env somedir t_test.sh     # a directory
Error: cannot read the bootstrap file: 'somedir'.

$ bashunit --env unread.sh t_test.sh   # exists, mode 000
Error: cannot read the bootstrap file: 'unread.sh'.

$ bashunit --env nope.sh t_test.sh     # does not exist
Error: cannot read the bootstrap file: 'nope.sh'.

It is accurate for exactly one of them. A directory is readable — the check that rejects it is -f, not -r — and for a path that does not exist, "cannot read" understates "is not there". Pointing --env at a directory (--env tests/, --boot config/) or mistyping a filename are both ordinary mistakes, and the message sends the reader to permissions in either case.

/dev/null is rejected the same way, which is how I noticed: it is readable and the message says otherwise.

Fix

Name the actual cause, the way install.sh does for its destination since #1197:

• does not exist → say so
• is a directory → say so (bashunit::main::report_path_is_a_directory already exists in the same file for this)
• exists but unreadable → the current message, now true

The --env space-split explanation added in #1247 stays as-is on top.

Related

Same class as #1197 (install destinations), #1221 (advice naming a flag that does not exist) and #1247 (the split that made a real file look missing).

[Chemaclass]

Done in #1264 (merged).