test: improve known broken tests support

There is existing support for broken tests.  But it is not convenient
to use.  The primary issue is that we have to maintain a set of
test_expect_*_failure functions which are equivalent to the normal
test_expect_* counterparts except for what functions are called for
result reporting.  The patch adds test_subtest_known_broken function
which marks a subset as broken, making the normal test_expect_*
functions behave as test_expect_*_failure.  All test_expect_*_failure
functions are removed.  Test_known_broken_failure_ is changed to
format details the same way as test_failure_ does.

Another benefit of this change is that the diff when a broken test is
fixed would be small and nice.

Documentation is updated accordingly.

test/README

@@ -132,20 +132,19 @@ library for your script to use.
    <script>.  If it yields success, test is considered
    successful.  <message> should state what it is testing.
 
- test_expect_failure <message> <script>
-
-   This is NOT the opposite of test_expect_success, but is used
-   to mark a test that demonstrates a known breakage.  Unlike
-   the usual test_expect_success tests, which say "ok" on
-   success and "FAIL" on failure, this will say "FIXED" on
-   success and "still broken" on failure.  Failures from these
-   tests won't cause -i (immediate) to stop.
-
  test_begin_subtest <message>
 
    Set the test description message for a subsequent test_expect_equal
    invocation (see below).
 
+ test_subtest_known_broken
+
+   Mark the current test as broken.  Such tests are expected to fail.
+   Unlike the normal tests, which say "PASS" on success and "FAIL" on
+   failure, these will say "FIXED" on success and "BROKEN" on failure.
+   Failures from these tests won't cause -i (immediate) to stop.  A
+   test must call this before any test_expect_* function.
+
  test_expect_equal <output> <expected>
 
    This is an often-used convenience function built on top of

test/test-lib.sh

@@ -424,6 +424,7 @@ test_begin_subtest ()
 	error "bug in test script: Missing test_expect_equal in ${BASH_SOURCE[1]}:${BASH_LINENO[0]}"
     fi
     test_subtest_name="$1"
+    test_subtest_known_broken_=
     # Remember stdout and stderr file descriptors and redirect test
     # output to the previously prepared file descriptors 3 and 4 (see
     # below)
@@ -484,29 +485,6 @@ test_expect_equal_file ()
     fi
 }
 
-test_expect_equal_failure ()
-{
-	exec 1>&6 2>&7		# Restore stdout and stderr
-	inside_subtest=
-	test "$#" = 3 && { prereq=$1; shift; } || prereq=
-	test "$#" = 2 ||
-	error "bug in the test script: not 2 or 3 parameters to test_expect_equal"
-
-	output="$1"
-	expected="$2"
-	if ! test_skip "$@"
-	then
-		if [ "$output" = "$expected" ]; then
-			test_known_broken_ok_ "$test_subtest_name"
-		else
-			test_known_broken_failure_ "$test_subtest_name"
-			testname=$this_test.$test_count
-			echo "$expected" > $testname.expected
-			echo "$output" > $testname.output
-		fi
-    fi
-}
-
 NOTMUCH_NEW ()
 {
     notmuch new | grep -v -E -e '^Processed [0-9]*( total)? file|Found [0-9]* total file'
@@ -568,19 +546,31 @@ test_have_prereq () {
 # the text_expect_* functions instead.
 
 test_ok_ () {
+	if test "$test_subtest_known_broken_" = "t"; then
+		test_known_broken_ok_ "$@"
+		return
+	fi
 	test_success=$(($test_success + 1))
 	say_color pass "%-6s" "PASS"
 	echo " $@"
 }
 
 test_failure_ () {
+	if test "$test_subtest_known_broken_" = "t"; then
+		test_known_broken_failure_ "$@"
+		return
+	fi
 	test_failure=$(($test_failure + 1))
-	say_color error "%-6s" "FAIL"
-	echo " $1"
-	shift
+	test_failure_message_ "FAIL" "$@"
+	test "$immediate" = "" || { GIT_EXIT_OK=t; exit 1; }
+}
+
+test_failure_message_ () {
+	say_color error "%-6s" "$1"
+	echo " $2"
+	shift 2
 	echo "$@" | sed -e 's/^/	/'
 	if test "$verbose" != "t"; then cat test.output; fi
-	test "$immediate" = "" || { GIT_EXIT_OK=t; exit 1; }
 }
 
 test_known_broken_ok_ () {
@@ -591,8 +581,7 @@ test_known_broken_ok_ () {
 
 test_known_broken_failure_ () {
 	test_broken=$(($test_broken+1))
-	say_color pass "%-6s" "BROKEN"
-	echo " $@"
+	test_failure_message_ "BROKEN" "$@"
 }
 
 test_debug () {
@@ -636,20 +625,8 @@ test_skip () {
 	esac
 }
 
-test_expect_failure () {
-	test "$#" = 3 && { prereq=$1; shift; } || prereq=
-	test "$#" = 2 ||
-	error "bug in the test script: not 2 or 3 parameters to test-expect-failure"
-	if ! test_skip "$@"
-	then
-		test_run_ "$2"
-		if [ "$?" = 0 -a "$eval_ret" = 0 ]
-		then
-			test_known_broken_ok_ "$1"
-		else
-			test_known_broken_failure_ "$1"
-		fi
-	fi
+test_subtest_known_broken () {
+	test_subtest_known_broken_=t
 }
 
 test_expect_success () {