Re: [PATCH 05/16] test-lib: Infrastructure to test and check for prerequisites

> Some tests can be run only if a particular prerequisite is available. For
> example, some tests require that an UTF-8 locale is available. Here we
> introduce functions that are used in this way:
>
> 1. Insert code that checks whether the prerequisite is available. If it is,
>    call test_set_prereq with an arbitrary tag name that subsequently can be
>    used to check for the prerequisite:
>
>       case $LANG in
>       *.utf-8)
>             test_set_prereq UTF8
>             ;;
>       esac
>
> 2. In the calls to test_expect_success pass the tag name:
>
>       test_expect_success UTF8 '...description...' '...tests...'
>
> 3. There is an auxiliary predicate that can be used anywhere to test for
>    a prerequisite explicitly:
>
>       if test_have_prereq UTF8
>       then
>             ...code to be skipped if prerequisite is not available...
>       fi
>
> Signed-off-by: Johannes Sixt <j6t@kdbg.org>