fixup! tests: include detailed trace logs with --write-junit-xml upon failure

The `cut -c` approach is *per line*, not *per file* as I had thought. So
it does not work...

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

t/helper/test-path-utils.c

@@ -311,6 +311,26 @@ int cmd__path_utils(int argc, const char **argv)
 		return !!res;
 	}
 
+	if (argc == 4 && !strcmp(argv[1], "skip-n-bytes")) {
+		int fd = open(argv[2], O_RDONLY), offset = atoi(argv[3]);
+		char buffer[65536];
+
+		if (fd < 0)
+			die_errno("could not open '%s'", argv[2]);
+		if (lseek(fd, offset, SEEK_SET) < 0)
+			die_errno("could not skip %d bytes", offset);
+		for (;;) {
+			ssize_t count = read(fd, buffer, sizeof(buffer));
+			if (count < 0)
+				die_errno("could not read '%s'", argv[2]);
+			if (!count)
+				break;
+			write(1, buffer, count);
+		}
+		close(fd);
+		return 0;
+	}
+
 	if (argc > 5 && !strcmp(argv[1], "slice-tests")) {
 		int res = 0;
 		long offset, stride, i;

t/test-lib.sh

@@ -518,7 +518,8 @@ test_failure_ () {
 		junit_insert="$junit_insert $(xml_attr_encode \
 			"$(if test -n "$GIT_TEST_TEE_OUTPUT_FILE"
 			   then
-				cut -c "$GIT_TEST_TEE_OFFSET-" <"$GIT_TEST_TEE_OUTPUT_FILE"
+				test-tool path-utils skip-n-bytes \
+					"$GIT_TEST_TEE_OUTPUT_FILE" $GIT_TEST_TEE_OFFSET
 			   else
 				printf '%s\n' "$@" | sed 1d
 			   fi)")"
@@ -823,6 +824,11 @@ test_finish_ () {
 	echo >&3 ""
 	maybe_teardown_valgrind
 	maybe_teardown_verbose
+	if test -n "$GIT_TEST_TEE_OFFSET"
+	then
+		GIT_TEST_TEE_OFFSET=$(test-tool path-utils file-size \
+			"$GIT_TEST_TEE_OUTPUT_FILE")
+	fi
 }
 
 test_skip () {
@@ -900,11 +906,6 @@ write_junit_xml_testcase () {
 	write_junit_xml "$(printf '%s\n' \
 		"    <testcase $junit_attrs>" "$@" "    </testcase>")"
 	junit_have_testcase=t
-	if test -n "$GIT_TEST_TEE_OUTPUT_FILE"
-	then
-		GIT_TEST_TEE_OFFSET=$(test-tool path-utils file-size \
-			"$GIT_TEST_TEE_OUTPUT_FILE")
-	fi
 }
 
 test_done () {
@@ -1198,7 +1199,6 @@ then
 	if test -n "$GIT_TEST_TEE_OUTPUT_FILE"
 	then
 		GIT_TEST_TEE_OFFSET=0
-		GIT_TEST_TEE_ERR_OFFSET=0
 	fi
 fi