Re: [PATCH 1/1] t: update path checks using test_path helpers

[Junio C Hamano <gitster@pobox.com>]

Solly <solobarine@gmail.com> writes:

> Subject: Re: [PATCH 1/1] t: update path checks using test_path helpers

Using "t2401:" instead of "t:" would give you a bit more
information.

> Update old-style shell path checks to use the modern test
> helpers 'test_path_is_file' and 'test_path_is_dir' for improved
> readability.

This gives a wrong justification.

For readability, "test -f tested-file" is plenty readable.  The
point of using test_path_is_file and its friends is to get better
runtime diagnosis.

Read the helper you are using and understand what it does and why it
does it (they are found in t/test-lib-functions.sh):

        # debugging-friendly alternatives to "test [-f|-d|-e]"
        # The commands test the existence or non-existence of $1
        test_path_is_file () {
                test "$#" -ne 1 && BUG "1 param"
                if ! test -f "$1"
                then
                        echo "File $1 doesn't exist"
                        false
                fi
        }

And imagine you wrote your test using this, perhaps like this:

        test_expect_success 'ensure hello.c exists' '
		test_path_is_file hello.c
        '

What happens when (1) hello.c does exist and (2) hello.c does not
exist?  If hello.c exists, "if ! test -f" fails, and the control
does not go inside of "then" part, hence the helper will succeed
silently.  If hello.c does not exist, it will say "File hello.c
doesn't exist".  The person who is running the test will be told why
the test failed (and the helper fails because it runs the 'false'
after giving the message).  And that is the value these helpers
offer.

Armed with that knowledge, you can tell that ...

>  	test_cmp expect actual &&
> -	! test -f .git/worktrees/abc &&
> -	! test -d .git/worktrees
> +	! test_path_is_file .git/worktrees/abc &&
> +	! test_path_is_dir .git/worktrees

... this is a bad rewrite, right?  The original wants to ensure that
a file .git/worktrees/abc does not exist.  You want the test to
be silent when the path is not a file (i.e. "as expected, nothing
interesting to see here"), and complain loudly when it *is* a file.

And your "! test_path_is_file .git/worktrees/abc" would not do that,
would it?  They report loudly in a wrong case!

In this case, both of them should probably become

	test_path_is_missing .git/worktrees/abc &&
	test_path_is_missing .git/worktrees

because the _intent_ of the test is NOT that it would be happy as
long as .git/worktrees/abc is not a file.  Even though the original
uses "! test -f", seeing a .git/worktrees/abc directory there is an
unexpected outcome of the test (you need to read what is being
tested to fully understand this kind of thing).

Hope this helps.