test: allow prerequisite to be evaluated lazily

The test prerequisite mechanism is a useful way to allow some tests
in a test script to be skipped in environments that do not support
certain features (e.g. it is pointless to attempt checking how well
symbolic links are handled by Git on filesystems that do not support
them).  It is OK for commonly used prerequisites to be always tested
during start-up of a test script by having a codeblock that tests a
feature and calls test_set_prereq, but for an uncommon feature,
forcing 90% of scripts to pay the same probing overhead for
prerequisite they do not care about is wasteful.

Introduce a mechanism to probe the prerequiste lazily.  Changes are:

- test_lazy_prereq () function, which takes the name of the
prerequisite it probes and the script to probe for it, is
added.  This only registers the name of the prerequiste that can
be lazily probed and the script to eval (without running).

- test_have_prereq() function (which is used by test_expect_success
and also can be called directly by test scripts) learns to look
at the list of prerequisites that can be lazily probed, and the
prerequisites that have already been probed that way.  When asked
for a prerequiste that can be but haven't been probed, the script
registered with an earlier call to test_lazy_prereq is evaluated
and the prerequisite is set.

- test_run_lazy_prereq_() function is a helper to run the probe
script with the same kind of sandbox as regular tests, helped by
Jeff King.

Update the codeblock to probe and set SYMLINKS prerequisite using
the new mechanism as an example.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/t/test-lib-functions.sh b/t/test-lib-functions.sh
index 4dc027d406d4bef7f51e51b0780361fdb6efff74..04b1a43ef2e79e1e89f5a8d330172d156a7d25ce 100644 (file)
--- a/t/test-lib-functions.sh
+++ b/t/test-lib-functions.sh
@@ -224,6 +224,32 @@ test_set_prereq () {
        satisfied_prereq="$satisfied_prereq$1 "
 }
 satisfied_prereq=" "
        satisfied_prereq="$satisfied_prereq$1 "
 }
 satisfied_prereq=" "

+lazily_testable_prereq= lazily_tested_prereq=
+
+# Usage: test_lazy_prereq PREREQ 'script'
+test_lazy_prereq () {
+       lazily_testable_prereq="$lazily_testable_prereq$1 "
+       eval test_prereq_lazily_$1=\$2
+}
+
+test_run_lazy_prereq_ () {
+       script='
+mkdir -p "$TRASH_DIRECTORY/prereq-test-dir" &&
+(
+       cd "$TRASH_DIRECTORY/prereq-test-dir" &&'"$2"'
+)'
+       say >&3 "checking prerequisite: $1"
+       say >&3 "$script"
+       test_eval_ "$script"
+       eval_ret=$?
+       rm -rf "$TRASH_DIRECTORY/prereq-test-dir"
+       if test "$eval_ret" = 0; then
+               say >&3 "prerequisite $1 ok"
+       else
+               say >&3 "prerequisite $1 not satisfied"
+       fi
+       return $eval_ret
+}

 
 test_have_prereq () {
        # prerequisites can be concatenated with ','
 
 test_have_prereq () {
        # prerequisites can be concatenated with ','


@@ -238,6 +264,22 @@ test_have_prereq () {
 
        for prerequisite
        do
 
        for prerequisite
        do

+               case " $lazily_tested_prereq " in
+               *" $prerequisite "*)
+                       ;;
+               *)
+                       case " $lazily_testable_prereq " in
+                       *" $prerequisite "*)
+                               eval "script=\$test_prereq_lazily_$prerequisite" &&
+                               if test_run_lazy_prereq_ "$prerequisite" "$script"
+                               then
+                                       test_set_prereq $prerequisite
+                               fi
+                               lazily_tested_prereq="$lazily_tested_prereq$prerequisite "
+                       esac
+                       ;;
+               esac
+

                total_prereq=$(($total_prereq + 1))
                case "$satisfied_prereq" in
                *" $prerequisite "*)
                total_prereq=$(($total_prereq + 1))
                case "$satisfied_prereq" in
                *" $prerequisite "*)

diff --git a/t/test-lib.sh b/t/test-lib.sh
index bb4f8865b2628665f4adbf9ceef03d5a9081e244..35739b9fbe632e59275ab1365f8ae85cce4618d0 100644 (file)
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -659,9 +659,10 @@ test_i18ngrep () {
        fi
 }
 
        fi
 }
 

-# test whether the filesystem supports symbolic links
-ln -s x y 2>/dev/null && test -h y 2>/dev/null && test_set_prereq SYMLINKS
-rm -f y
+test_lazy_prereq SYMLINKS '
+       # test whether the filesystem supports symbolic links
+       ln -s x y && test -h y
+'

 
 # When the tests are run as root, permission tests will report that
 # things are writable when they shouldn't be.
 
 # When the tests are run as root, permission tests will report that
 # things are writable when they shouldn't be.