t4027,4041: Use test -s to test for an empty file

The tests used a mixture of 'echo -n' (which is non-portable) and either
test_cmp or diff to check if a file is empty.  The much easier and portable
method to check for an empty file is '! test -s'

While we're in t4027, there was an excess test_done.  Remove it.

Signed-off-by: Brian Gernhardt <brian@gernhardtsoftware.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t4027-diff-submodule.sh

@@ -105,15 +105,15 @@ test_expect_success 'git diff HEAD with dirty submodule (work tree, refs match)'
 	expect_from_to >expect.body $subprev $subprev-dirty &&
 	test_cmp expect.body actual.body &&
 	git diff --ignore-submodules HEAD >actual2 &&
-	echo -n "" | test_cmp - actual2 &&
+	! test -s actual2 &&
 	git diff --ignore-submodules=untracked HEAD >actual3 &&
 	sed -e "1,/^@@/d" actual3 >actual3.body &&
 	expect_from_to >expect.body $subprev $subprev-dirty &&
 	test_cmp expect.body actual3.body &&
 	git diff --ignore-submodules=dirty HEAD >actual4 &&
-	echo -n "" | test_cmp - actual4
+	! test -s actual4
 '
-test_done
+
 test_expect_success 'git diff HEAD with dirty submodule (index, refs match)' '
 	(
 		cd sub &&
@@ -139,11 +139,11 @@ test_expect_success 'git diff HEAD with dirty submodule (untracked, refs match)'
 	expect_from_to >expect.body $subprev $subprev-dirty &&
 	test_cmp expect.body actual.body &&
 	git diff --ignore-submodules=all HEAD >actual2 &&
-	echo -n "" | test_cmp - actual2 &&
+	! test -s actual2 &&
 	git diff --ignore-submodules=untracked HEAD >actual3 &&
-	echo -n "" | test_cmp - actual3 &&
+	! test -s actual3 &&
 	git diff --ignore-submodules=dirty HEAD >actual4 &&
-	echo -n "" | test_cmp - actual4
+	! test -s actual4
 '
 
 test_expect_success 'git diff (empty submodule dir)' '

t/t4041-diff-submodule-option.sh

@@ -207,17 +207,17 @@ EOF
 
 test_expect_success 'submodule contains untracked content (untracked ignored)' "
 	git diff-index -p --ignore-submodules=untracked --submodule=log HEAD >actual &&
-	echo -n '' | diff actual -
+	! test -s actual
 "
 
 test_expect_success 'submodule contains untracked content (dirty ignored)' "
 	git diff-index -p --ignore-submodules=dirty --submodule=log HEAD >actual &&
-	echo -n '' | diff actual -
+	! test -s actual
 "
 
 test_expect_success 'submodule contains untracked content (all ignored)' "
 	git diff-index -p --ignore-submodules=all --submodule=log HEAD >actual &&
-	echo -n '' | diff actual -
+	! test -s actual
 "
 
 test_expect_success 'submodule contains untracked and modifed content' "
@@ -240,13 +240,13 @@ EOF
 test_expect_success 'submodule contains untracked and modifed content (dirty ignored)' "
 	echo new > sm1/foo6 &&
 	git diff-index -p --ignore-submodules=dirty --submodule=log HEAD >actual &&
-	echo -n '' | diff actual -
+	! test -s actual
 "
 
 test_expect_success 'submodule contains untracked and modifed content (all ignored)' "
 	echo new > sm1/foo6 &&
 	git diff-index -p --ignore-submodules --submodule=log HEAD >actual &&
-	echo -n '' | diff actual -
+	! test -s actual
 "
 
 test_expect_success 'submodule contains modifed content' "
@@ -295,7 +295,7 @@ EOF
 
 test_expect_success 'modified submodule contains untracked content (all ignored)' "
 	git diff-index -p --ignore-submodules=all --submodule=log HEAD >actual &&
-	echo -n '' | diff actual -
+	! test -s actual
 "
 
 test_expect_success 'modified submodule contains untracked and modifed content' "
@@ -331,7 +331,7 @@ EOF
 test_expect_success 'modified submodule contains untracked and modifed content (all ignored)' "
 	echo modification >> sm1/foo6 &&
 	git diff-index -p --ignore-submodules --submodule=log HEAD >actual &&
-	echo -n '' | diff actual -
+	! test -s actual
 "
 
 test_expect_success 'modified submodule contains modifed content' "