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, 7 insertions, 11 deletions

diff --git a/t/t7811-grep-open.sh b/t/t7811-grep-open.sh
index e1951a5cbb..d1ebfd88c7 100755
--- a/t/t7811-grep-open.sh
+++ b/t/t7811-grep-open.sh
@@ -51,14 +51,13 @@ test_expect_success SIMPLEPAGER 'git grep -O' '
 	grep.h
 	EOF
 	echo grep.h >expect.notless &&
-	>empty &&
 
 	PATH=.:$PATH git grep -O GREP_PATTERN >out &&
 	{
 		test_cmp expect.less pager-args ||
 		test_cmp expect.notless pager-args
 	} &&
-	test_cmp empty out
+	test_must_be_empty out
 '
 
 test_expect_success 'git grep -O --cached' '
@@ -72,7 +71,6 @@ test_expect_success 'git grep -O --no-index' '
 	grep.h
 	untracked
 	EOF
-	>empty &&
 
 	(
 		GIT_PAGER='\''printf "%s\n" >pager-args'\'' &&
@@ -80,7 +78,7 @@ test_expect_success 'git grep -O --no-index' '
 		git grep --no-index -O GREP_PATTERN >out
 	) &&
 	test_cmp expect pager-args &&
-	test_cmp empty out
+	test_must_be_empty out
 '
 
 test_expect_success 'setup: fake "less"' '
@@ -96,15 +94,14 @@ test_expect_success 'git grep -O jumps to line in less' '
 	+/*GREP_PATTERN
 	grep.h
 	EOF
-	>empty &&
 
 	GIT_PAGER=./less git grep -O GREP_PATTERN >out &&
 	test_cmp expect actual &&
-	test_cmp empty out &&
+	test_must_be_empty out &&
 
 	git grep -O./less GREP_PATTERN >out2 &&
 	test_cmp expect actual &&
-	test_cmp empty out2
+	test_must_be_empty out2
 '
 
 test_expect_success 'modified file' '
@@ -122,7 +119,7 @@ test_expect_success 'modified file' '
 	test_when_finished "git checkout HEAD unrelated" &&
 	GIT_PAGER=./less git grep -F -O "enum grep_pat_token" >out &&
 	test_cmp expect actual &&
-	test_cmp empty out
+	test_must_be_empty out
 '
 
 test_expect_success 'copes with color settings' '
@@ -138,7 +135,6 @@ test_expect_success 'copes with color settings' '
 test_expect_success 'run from subdir' '
 	rm -f actual &&
 	echo grep.c >expect &&
-	>empty &&
 
 	(
 		cd subdir &&
@@ -156,8 +152,8 @@ test_expect_success 'run from subdir' '
 		;;
 	esac &&
 	test_cmp expect args &&
-	test_cmp empty out &&
-	test_cmp empty out2
+	test_must_be_empty out &&
+	test_must_be_empty out2
 '
 
 test_done