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>

1 files changed, 15 insertions, 0 deletions

diff --git a/t/t0000-basic.sh b/t/t0000-basic.sh
index ddcd5b0efb..c53de1f212 100755
--- a/t/t0000-basic.sh
+++ b/t/t0000-basic.sh
@@ -57,6 +57,21 @@ test_expect_failure 'pretend we have a known breakage' '
 test_expect_failure 'pretend we have fixed a known breakage' '
     :
 '
+test_set_prereq HAVEIT
+haveit=no
+test_expect_success HAVEIT 'test runs if prerequisite is satisfied' '
+    test_have_prereq HAVEIT &&
+    haveit=yes
+'
+donthaveit=yes
+test_expect_success DONTHAVEIT 'unmet prerequisite causes test to be skipped' '
+    donthaveit=no
+'
+if test $haveit$donthaveit != yesyes
+then
+	say "bug in test framework: prerequisite tags do not work reliably"
+	exit 1
+fi
 
 ################################################################
 # Basics of the basics