tests: use 'test_must_be_empty' instead of 'test_cmp <empty> <out>'

Using 'test_must_be_empty' is shorter and more idiomatic than

  >empty &&
  test_cmp empty out

as it saves the creation of an empty file.  Furthermore, sometimes the
expected empty file doesn't have such a descriptive name like 'empty',
and its creation is far away from the place where it's finally used
for comparison (e.g. in 't7600-merge.sh', where two expected empty
files are created in the 'setup' test, but are used only about 500
lines later).

These cases were found by instrumenting 'test_cmp' to error out the
test script when it's used to compare empty files, and then converted
manually.

Note that even after this patch there still remain a lot of cases
where we use 'test_cmp' to check empty files:

  - Sometimes the expected output is not hard-coded in the test, but
    'test_cmp' is used to ensure that two similar git commands produce
    the same output, and that output happens to be empty, e.g. the
    test 'submodule update --merge  - ignores --merge  for new
    submodules' in 't7406-submodule-update.sh'.

  - Repetitive common tasks, including preparing the expected results
    and running 'test_cmp', are often extracted into a helper
    function, and some of this helper's callsites expect no output.

  - For the same reason as above, the whole 'test_expect_success'
    block is within a helper function, e.g. in 't3070-wildmatch.sh'.

  - Or 'test_cmp' is invoked in a loop, e.g. the test 'cvs update
    (-p)' in 't9400-git-cvsserver-server.sh'.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 2 insertions, 6 deletions

diff --git a/t/t7004-tag.sh b/t/t7004-tag.sh
index 93a6694f0e..2e17cdb084 100755
--- a/t/t7004-tag.sh
+++ b/t/t7004-tag.sh
@@ -325,11 +325,10 @@ test_expect_success \
 	test_cmp expect actual
 '
 
->expect
 test_expect_success \
 	'listing tags using v.* should print nothing because none have v.' '
 	git tag -l "v.*" > actual &&
-	test_cmp expect actual
+	test_must_be_empty actual
 '
 
 cat >expect <<EOF
@@ -1498,12 +1497,9 @@ test_expect_success 'inverse of the last test, with --no-contains' "
 	test_cmp expected actual
 "
 
-cat > expected <<EOF
-EOF
-
 test_expect_success 'checking that third commit has no tags' "
 	git tag -l --contains $hash3 v* >actual &&
-	test_cmp expected actual
+	test_must_be_empty actual
 "
 
 cat > expected <<EOF