Re: [PATCH v2] test_cmp: diagnose incorrect arguments

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

Eric Sunshine <sunshine@sunshineco.com> writes:

> Under normal circumstances, if a test author misspells a filename passed
> to test_cmp(), the error is quickly discovered when the test fails
> unexpectedly due to test_cmp() being unable to find the file. However,
> if the test is expected to fail, as with test_expect_failure(), a
> misspelled filename as argument to test_cmp() will go unnoticed since
> the test will indeed fail, but for the wrong reason. Make it easier for
> test authors to discover such problems early by sanity-checking the
> arguments to test_cmp(). To avoid penalizing all clients of test_cmp()
> in the general case, only check for missing files if the comparison
> fails.
>
> While at it, make test_cmp_bin() sanity-check its arguments, as well.
>
> Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
> ---

The motivation makes quite a lot of sense.

I suspect that it is a bug to use "-", i.e. "read from the standard
input", for "$2", because

 (1) if it is used for the expected output, we got the comparison in
     the wrong direction;

 (2) if it is used for the actual output, we have a command whose
     output we are interested in on the upstream side of a pipe to
     discard its exit status.

but I'll let it pass.

> diff --git a/t/test-lib-functions.sh b/t/test-lib-functions.sh
> index b791933ffd..a12d6a3fc9 100644
> --- a/t/test-lib-functions.sh
> +++ b/t/test-lib-functions.sh
> @@ -952,7 +952,13 @@ test_expect_code () {
>  # - not all diff versions understand "-u"
>  
>  test_cmp() {
> -	eval "$GIT_TEST_CMP" '"$@"'
> +	test $# -eq 2 || BUG "test_cmp requires two arguments"
> +	if ! eval "$GIT_TEST_CMP" '"$@"'
> +	then
> +		test "x$1" = x- || test -e "$1" || BUG "test_cmp '$1' missing"
> +		test "x$2" = x- || test -e "$2" || BUG "test_cmp '$2' missing"
> +		return 1
> +	fi
>  }
>  
>  # Check that the given config key has the expected value.
> @@ -981,7 +987,13 @@ test_cmp_config() {
>  # test_cmp_bin - helper to compare binary files
>  
>  test_cmp_bin() {
> -	cmp "$@"
> +	test $# -eq 2 || BUG "test_cmp_bin requires two arguments"
> +	if ! cmp "$@"
> +	then
> +		test "x$1" = x- || test -e "$1" || BUG "test_cmp_bin '$1' missing"
> +		test "x$2" = x- || test -e "$2" || BUG "test_cmp_bin '$2' missing"
> +		return 1
> +	fi
>  }
>  
>  # Use this instead of test_cmp to compare files that contain expected and