t/t4004-diff-rename-symlink.sh: use three-arg <prereq>

Change the tests that skipped due to unavailable SYMLINKS support to
use the three-arg prereq form of test_expect_success.

This is like the "tests: implicitly skip SYMLINKS tests using
<prereq>" change, but I needed to create an additional test for some
setup code. It's in a separate change as suggested by Jonathan Nieder
for ease of reviewing.

    Date: Tue, 27 Jul 2010 16:17:37 -0500
    From: Jonathan Nieder <jrnieder@gmail.com>
    Message-ID: <20100727211737.GA11768@burratino>
    In-Reply-To: <1280265254-19642-2-git-send-email-avarab@gmail.com>
    Subject: Re: [PATCH 1/4] tests: implicitly skip SYMLINKS tests using <prereq>

    Ævar Arnfjörð Bjarmason wrote:

    > +++ b/t/t4004-diff-rename-symlink.sh
    > @@ -40,8 +34,9 @@ test_expect_success \
    >  # rezrov and nitfol are rename/copy of frotz and bozbar should be
    >  # a new creation.
    >
    > -GIT_DIFF_OPTS=--unified=0 git diff-index -M -p $tree >current
    > -cat >expected <<\EOF
    > +test_expect_success SYMLINKS 'setup diff output' "
    > +    GIT_DIFF_OPTS=--unified=0 git diff-index -M -p $tree >current
    > +    cat >expected <<\EOF
    >  diff --git a/bozbar b/bozbar
    >  new file mode 120000
    >  --- /dev/null

    Probably belongs in a separate patch.  More importantly, it is missing
    &&-chaining (not a regression, but it is best to set a good example).

Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t4004-diff-rename-symlink.sh

@@ -12,13 +12,7 @@ by an edit for them.
 . ./test-lib.sh
 . "$TEST_DIRECTORY"/diff-lib.sh
 
-if ! test_have_prereq SYMLINKS
-then
-	skip_all='Symbolic links not supported, skipping tests.'
-	test_done
-fi
-
-test_expect_success \
+test_expect_success SYMLINKS \
     'prepare reference tree' \
     'echo xyzzy | tr -d '\\\\'012 >yomin &&
      ln -s xyzzy frotz &&
@@ -26,7 +20,7 @@ test_expect_success \
     tree=$(git write-tree) &&
     echo $tree'
 
-test_expect_success \
+test_expect_success SYMLINKS \
     'prepare work tree' \
     'mv frotz rezrov &&
      rm -f yomin &&
@@ -40,8 +34,9 @@ test_expect_success \
 # rezrov and nitfol are rename/copy of frotz and bozbar should be
 # a new creation.
 
-GIT_DIFF_OPTS=--unified=0 git diff-index -M -p $tree >current
-cat >expected <<\EOF
+test_expect_success SYMLINKS 'setup diff output' "
+    GIT_DIFF_OPTS=--unified=0 git diff-index -M -p $tree >current &&
+    cat >expected <<\EOF
 diff --git a/bozbar b/bozbar
 new file mode 120000
 --- /dev/null
@@ -65,8 +60,9 @@ deleted file mode 100644
 -xyzzy
 \ No newline at end of file
 EOF
+"
 
-test_expect_success \
+test_expect_success SYMLINKS \
     'validate diff output' \
     'compare_diff_patch current expected'