t4014: check for empty files from git format-patch --stdout

Most kinds of failure in 'git format-patch --stdout >output' will
result in an empty 'output'.  This slips past checks that only verify
absence of output, such as the '! grep ...' that are quite prevalent
in t4014.

Introduce a helper check_patch() that checks that at least From, Date
and Subject are present, thus making sure it looks vaguely like a
patch (or cover letter) email.  Then insert calls to it in all tests
that do have positive checks for content.

This makes two of the tests fail.  Mark them as such; they'll be
fixed in a moment.

Signed-off-by: Thomas Rast <trast@student.ethz.ch>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t4014-format-patch.sh

@@ -179,12 +179,21 @@ test_expect_success 'configuration To: header' '
 	grep "^To: R. E. Cipient <rcipient@example.com>\$" patch9
 '
 
+# check_patch <patch>: Verify that <patch> looks like a half-sane
+# patch email to avoid a false positive with !grep
+check_patch () {
+	grep -e "^From:" "$1" &&
+	grep -e "^Date:" "$1" &&
+	grep -e "^Subject:" "$1"
+}
+
 test_expect_success '--no-to overrides config.to' '
 
 	git config --replace-all format.to \
 		"R. E. Cipient <rcipient@example.com>" &&
 	git format-patch --no-to --stdout master..side |
 	sed -e "/^\$/q" >patch10 &&
+	check_patch patch10 &&
 	! grep "^To: R. E. Cipient <rcipient@example.com>\$" patch10
 '
 
@@ -195,6 +204,7 @@ test_expect_success '--no-to and --to replaces config.to' '
 	git format-patch --no-to --to="Someone Else <else@out.there>" \
 		--stdout master..side |
 	sed -e "/^\$/q" >patch11 &&
+	check_patch patch11 &&
 	! grep "^To: Someone <someone@out.there>\$" patch11 &&
 	grep "^To: Someone Else <else@out.there>\$" patch11
 '
@@ -205,15 +215,17 @@ test_expect_success '--no-cc overrides config.cc' '
 		"C. E. Cipient <rcipient@example.com>" &&
 	git format-patch --no-cc --stdout master..side |
 	sed -e "/^\$/q" >patch12 &&
+	check_patch patch12 &&
 	! grep "^Cc: C. E. Cipient <rcipient@example.com>\$" patch12
 '
 
-test_expect_success '--no-add-headers overrides config.headers' '
+test_expect_failure '--no-add-headers overrides config.headers' '
 
 	git config --replace-all format.headers \
 		"Header1: B. E. Cipient <rcipient@example.com>" &&
 	git format-patch --no-add-headers --stdout master..side |
 	sed -e "/^\$/q" >patch13 &&
+	check_patch patch13 &&
 	! grep "^Header1: B. E. Cipient <rcipient@example.com>\$" patch13
 '
 
@@ -480,6 +492,7 @@ test_expect_success 'cover-letter inherits diff options' '
 	git mv file foo &&
 	git commit -m foo &&
 	git format-patch --cover-letter -1 &&
+	check_patch 0000-cover-letter.patch &&
 	! grep "file => foo .* 0 *\$" 0000-cover-letter.patch &&
 	git format-patch --cover-letter -1 -M &&
 	grep "file => foo .* 0 *\$" 0000-cover-letter.patch
@@ -657,6 +670,7 @@ test_expect_success 'format-patch --no-signature ignores format.signature' '
 	git config format.signature "config sig" &&
 	git format-patch --stdout --signature="my sig" --no-signature \
 		-1 >output &&
+	check_patch output &&
 	! grep "config sig" output &&
 	! grep "my sig" output &&
 	! grep "^-- \$" output
@@ -673,17 +687,20 @@ test_expect_success 'format-patch --signature --cover-letter' '
 test_expect_success 'format.signature="" supresses signatures' '
 	git config format.signature "" &&
 	git format-patch --stdout -1 >output &&
+	check_patch output &&
 	! grep "^-- \$" output
 '
 
 test_expect_success 'format-patch --no-signature supresses signatures' '
 	git config --unset-all format.signature &&
 	git format-patch --stdout --no-signature -1 >output &&
+	check_patch output &&
 	! grep "^-- \$" output
 '
 
-test_expect_success 'format-patch --signature="" supresses signatures' '
+test_expect_failure 'format-patch --signature="" supresses signatures' '
 	git format-patch --signature="" -1 >output &&
+	check_patch output &&
 	! grep "^-- \$" output
 '