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, 27 deletions

diff --git a/t/t4300-merge-tree.sh b/t/t4300-merge-tree.sh
index 9015e47654..d87cc7d9ef 100755
--- a/t/t4300-merge-tree.sh
+++ b/t/t4300-merge-tree.sh
@@ -25,25 +25,19 @@ EXPECTED
 '
 
 test_expect_success 'file add !A, B' '
-	cat >expected <<\EXPECTED &&
-EXPECTED
-
 	git reset --hard initial &&
 	test_commit "add-not-a-b" "ONE" "AAA" &&
 	git merge-tree initial add-not-a-b initial >actual &&
-	test_cmp expected actual
+	test_must_be_empty actual
 '
 
 test_expect_success 'file add A, B (same)' '
-	cat >expected <<\EXPECTED &&
-EXPECTED
-
 	git reset --hard initial &&
 	test_commit "add-a-b-same-A" "ONE" "AAA" &&
 	git reset --hard initial &&
 	test_commit "add-a-b-same-B" "ONE" "AAA" &&
 	git merge-tree initial add-a-b-same-A add-a-b-same-B >actual &&
-	test_cmp expected actual
+	test_must_be_empty actual
 '
 
 test_expect_success 'file add A, B (different)' '
@@ -68,13 +62,10 @@ EXPECTED
 '
 
 test_expect_success 'file change A, !B' '
-	cat >expected <<\EXPECTED &&
-EXPECTED
-
 	git reset --hard initial &&
 	test_commit "change-a-not-b" "initial-file" "BBB" &&
 	git merge-tree initial change-a-not-b initial >actual &&
-	test_cmp expected actual
+	test_must_be_empty actual
 '
 
 test_expect_success 'file change !A, B' '
@@ -94,15 +85,12 @@ EXPECTED
 '
 
 test_expect_success 'file change A, B (same)' '
-	cat >expected <<\EXPECTED &&
-EXPECTED
-
 	git reset --hard initial &&
 	test_commit "change-a-b-same-A" "initial-file" "AAA" &&
 	git reset --hard initial &&
 	test_commit "change-a-b-same-B" "initial-file" "AAA" &&
 	git merge-tree initial change-a-b-same-A change-a-b-same-B >actual &&
-	test_cmp expected actual
+	test_must_be_empty actual
 '
 
 test_expect_success 'file change A, B (different)' '
@@ -175,16 +163,13 @@ AAA" &&
 '
 
 test_expect_success 'file remove A, !B' '
-	cat >expected <<\EXPECTED &&
-EXPECTED
-
 	git reset --hard initial &&
 	test_commit "rm-a-not-b-base" "ONE" "AAA" &&
 	git rm ONE &&
 	git commit -m "rm-a-not-b" &&
 	git tag "rm-a-not-b" &&
 	git merge-tree rm-a-not-b-base rm-a-not-b rm-a-not-b-base >actual &&
-	test_cmp expected actual
+	test_must_be_empty actual
 '
 
 test_expect_success 'file remove !A, B' '
@@ -206,16 +191,13 @@ EXPECTED
 '
 
 test_expect_success 'file remove A, B (same)' '
-	cat >expected <<\EXPECTED &&
-EXPECTED
-
 	git reset --hard initial &&
 	test_commit "rm-a-b-base" "ONE" "AAA" &&
 	git rm ONE &&
 	git commit -m "rm-a-b" &&
 	git tag "rm-a-b" &&
 	git merge-tree rm-a-b-base rm-a-b rm-a-b >actual &&
-	test_cmp expected actual
+	test_must_be_empty actual
 '
 
 test_expect_success 'file change A, remove B' '
@@ -260,13 +242,11 @@ EXPECTED
 '
 
 test_expect_success 'tree add A, B (same)' '
-	cat >expect <<-\EOF &&
-	EOF
 	git reset --hard initial &&
 	mkdir sub &&
 	test_commit "add sub/file" "sub/file" "file" add-tree-A &&
 	git merge-tree initial add-tree-A add-tree-A >actual &&
-	test_cmp expect actual
+	test_must_be_empty actual
 '
 
 test_expect_success 'tree add A, B (different)' '