diff --git a/test/sharness.sh b/test/sharness.sh
index 1d57ce9..ace5a5b 100644
--- a/test/sharness.sh
+++ b/test/sharness.sh
@@ -1,4 +1,4 @@
-#!/bin/sh
+# Sharness test framework.
 #
 # Copyright (c) 2011-2012 Mathias Lafeldt
 # Copyright (c) 2005-2012 Git project
@@ -22,10 +22,22 @@ SHARNESS_VERSION="1.0.0"
 export SHARNESS_VERSION
 
 # Public: The file extension for tests.  By default, it is set to "t".
-: ${SHARNESS_TEST_EXTENSION:=t}
+: "${SHARNESS_TEST_EXTENSION:=t}"
 export SHARNESS_TEST_EXTENSION
 
-#  Reset TERM to original terminal if found, otherwise save orignal TERM
+# Public: Root directory containing tests. Tests can override this variable,
+# e.g. for testing Sharness itself.
+if test -z "$SHARNESS_TEST_DIRECTORY"
+then
+	SHARNESS_TEST_DIRECTORY=$(pwd)
+else
+	# ensure that SHARNESS_TEST_DIRECTORY is an absolute path so that it
+	# is valid even if the current working directory is changed
+	SHARNESS_TEST_DIRECTORY=$(cd "$SHARNESS_TEST_DIRECTORY" && pwd) || exit 1
+fi
+export SHARNESS_TEST_DIRECTORY
+
+#  Reset TERM to original terminal if found, otherwise save original TERM
 [ "x" = "x$SHARNESS_ORIG_TERM" ] &&
 		SHARNESS_ORIG_TERM="$TERM" ||
 		TERM="$SHARNESS_ORIG_TERM"
@@ -33,23 +45,45 @@ export SHARNESS_TEST_EXTENSION
 export SHARNESS_ORIG_TERM
 
 # Export SHELL_PATH
-: ${SHELL_PATH:=$SHELL}
+: "${SHELL_PATH:=$SHELL}"
 export SHELL_PATH
 
+# if --tee was passed, write the output not only to the terminal, but
+# additionally to the file test-results/$BASENAME.out, too.
+case "$SHARNESS_TEST_TEE_STARTED, $* " in
+done,*)
+	# do not redirect again
+	;;
+*' --tee '*|*' --verbose-log '*)
+	mkdir -p "$SHARNESS_TEST_DIRECTORY/test-results"
+	BASE="$SHARNESS_TEST_DIRECTORY/test-results/$(basename "$0" ".$SHARNESS_TEST_EXTENSION")"
+
+	# Make this filename available to the sub-process in case it is using
+	# --verbose-log.
+	SHARNESS_TEST_TEE_OUTPUT_FILE="$BASE.out"
+	export SHARNESS_TEST_TEE_OUTPUT_FILE
+
+	# Truncate before calling "tee -a" to get rid of the results
+	# from any previous runs.
+	: >"$SHARNESS_TEST_TEE_OUTPUT_FILE"
+
+	(SHARNESS_TEST_TEE_STARTED="done" ${SHELL_PATH} "$0" "$@" 2>&1;
+	 echo $? >"$BASE.exit") | tee -a "$SHARNESS_TEST_TEE_OUTPUT_FILE"
+	test "$(cat "$BASE.exit")" = 0
+	exit
+	;;
+esac
+
 # For repeatability, reset the environment to a known state.
 # TERM is sanitized below, after saving color control sequences.
 LANG=C
 LC_ALL=C
-PAGER=cat
+PAGER="cat"
 TZ=UTC
 EDITOR=:
 export LANG LC_ALL PAGER TZ EDITOR
 unset VISUAL CDPATH GREP_OPTIONS
 
-# Line feed
-LF='
-'
-
 [ "x$TERM" != "xdumb" ] && (
 		[ -t 1 ] &&
 		tput bold >/dev/null 2>&1 &&
@@ -82,9 +116,14 @@ while test "$#" -ne 0; do
 		chain_lint=; shift ;;
 	--no-color)
 		color=; shift ;;
+	--tee)
+		shift ;; # was handled already
 	--root=*)
 		root=$(expr "z$1" : 'z[^=]*=\(.*\)')
 		shift ;;
+	--verbose-log)
+		verbose_log=t
+		shift ;;
 	*)
 		echo "error: unknown test option '$1'" >&2; exit 1 ;;
 	esac
@@ -109,18 +148,25 @@ if test -n "$color"; then
 	say_color_pass=$(tput setaf 2) # green
 	say_color_info=$(tput setaf 6) # cyan
 	say_color_reset=$(tput sgr0)
-	say_color_="" # no formatting for normal text
+	say_color_raw="" # no formatting for normal text
 	say_color() {
 		test -z "$1" && test -n "$quiet" && return
-		eval "say_color_color=\$say_color_$1"
+		case "$1" in
+			error) say_color_color=$say_color_error ;;
+			skip) say_color_color=$say_color_skip ;;
+			warn) say_color_color=$say_color_warn ;;
+			pass) say_color_color=$say_color_pass ;;
+			info) say_color_color=$say_color_info ;;
+			*) say_color_color=$say_color_raw ;;
+		esac
 		shift
-		printf "%s\\n" "$say_color_color$*$say_color_reset"
+		printf '%s%s%s\n' "$say_color_color" "$*" "$say_color_reset"
 	}
 else
 	say_color() {
 		test -z "$1" && test -n "$quiet" && return
 		shift
-		printf "%s\n" "$*"
+		printf '%s\n' "$*"
 	}
 fi
 
@@ -137,7 +183,7 @@ say() {
 	say_color info "$*"
 }
 
-test -n "$test_description" || error "Test script did not set test_description."
+test -n "${test_description:-}" || error "Test script did not set test_description."
 
 if test "$help" = "t"; then
 	echo "$test_description"
@@ -146,7 +192,11 @@ fi
 
 exec 5>&1
 exec 6<&0
-if test "$verbose" = "t"; then
+if test "$verbose_log" = "t"
+then
+	exec 3>>"$SHARNESS_TEST_TEE_OUTPUT_FILE" 4>&3
+elif test "$verbose" = "t"
+then
 	exec 4>&2 3>&1
 else
 	exec 4>/dev/null 3>/dev/null
@@ -177,7 +227,7 @@ trap 'die' EXIT
 # implicitly by specifying the prerequisite name in calls to test_expect_success
 # or test_expect_failure.
 #
-# $1 - Name of prerequiste (a simple word, in all capital letters by convention)
+# $1 - Name of prerequisite (a simple word, in all capital letters by convention)
 #
 # Examples
 #
@@ -214,7 +264,7 @@ test_have_prereq() {
 	# prerequisites can be concatenated with ','
 	save_IFS=$IFS
 	IFS=,
-	set -- $*
+	set -- $@
 	IFS=$save_IFS
 
 	total_prereq=0
@@ -231,7 +281,7 @@ test_have_prereq() {
 			negative_prereq=
 		esac
 
-		total_prereq=$(($total_prereq + 1))
+		total_prereq=$((total_prereq + 1))
 		case "$satisfied_prereq" in
 		*" $prerequisite "*)
 			satisfied_this_prereq=t
@@ -242,7 +292,7 @@ test_have_prereq() {
 
 		case "$satisfied_this_prereq,$negative_prereq" in
 		t,|,t)
-			ok_prereq=$(($ok_prereq + 1))
+			ok_prereq=$((ok_prereq + 1))
 			;;
 		*)
 			# Keep a list of missing prerequisites; restore
@@ -263,12 +313,12 @@ test_have_prereq() {
 # the text_expect_* functions instead.
 
 test_ok_() {
-	test_success=$(($test_success + 1))
-	say_color "" "ok $test_count - $@"
+	test_success=$((test_success + 1))
+	say_color "" "ok $test_count - $*"
 }
 
 test_failure_() {
-	test_failure=$(($test_failure + 1))
+	test_failure=$((test_failure + 1))
 	say_color error "not ok $test_count - $1"
 	shift
 	echo "$@" | sed -e 's/^/#	/'
@@ -276,13 +326,13 @@ test_failure_() {
 }
 
 test_known_broken_ok_() {
-	test_fixed=$(($test_fixed + 1))
-	say_color error "ok $test_count - $@ # TODO known breakage vanished"
+	test_fixed=$((test_fixed + 1))
+	say_color error "ok $test_count - $* # TODO known breakage vanished"
 }
 
 test_known_broken_failure_() {
-	test_broken=$(($test_broken + 1))
-	say_color warn "not ok $test_count - $@ # TODO known breakage"
+	test_broken=$((test_broken + 1))
+	say_color warn "not ok $test_count - $* # TODO known breakage"
 }
 
 # Public: Execute commands in debug mode.
@@ -351,7 +401,7 @@ test_run_() {
 }
 
 test_skip_() {
-	test_count=$(($test_count + 1))
+	test_count=$((test_count + 1))
 	to_skip=
 	for skp in $SKIP_TESTS; do
 		case $this_test.$test_count in
@@ -370,7 +420,7 @@ test_skip_() {
 			of_prereq=" of $test_prereq"
 		fi
 
-		say_color skip >&3 "skipping test: $@"
+		say_color skip >&3 "skipping test: $*"
 		say_color skip "ok $test_count # skip $1 (missing $missing_prereq${of_prereq})"
 		: true
 		;;
@@ -468,6 +518,44 @@ test_expect_failure() {
 	echo >&3 ""
 }
 
+# Public: Run test commands and expect anything from them. Used when a
+# test is not stable or not finished for some reason.
+#
+# When the test passed, an "ok" message is printed, but the number of
+# fixed tests is not incremented.
+#
+# When it failed, a "not ok ... # TODO known breakage" message is
+# printed, and the number of tests still broken is incremented.
+#
+# Failures from these tests won't cause --immediate to stop.
+#
+# Usually takes two arguments:
+# $1 - Test description
+# $2 - Commands to be executed.
+#
+# With three arguments, the first will be taken to be a prerequisite:
+# $1 - Comma-separated list of test prerequisites. The test will be skipped if
+#      not all of the given prerequisites are set. To negate a prerequisite,
+#      put a "!" in front of it.
+# $2 - Test description
+# $3 - Commands to be executed.
+#
+# Returns nothing.
+test_expect_unstable() {
+	test "$#" = 3 && { test_prereq=$1; shift; } || test_prereq=
+	test "$#" = 2 || error "bug in the test script: not 2 or 3 parameters to test_expect_unstable"
+	export test_prereq
+	if ! test_skip_ "$@"; then
+		say >&3 "checking unstable test: $2"
+		if test_run_ "$2" unstable; then
+			test_ok_ "$1"
+		else
+			test_known_broken_failure_ "$1"
+		fi
+	fi
+	echo >&3 ""
+}
+
 # Public: Run command and ensure that it fails in a controlled way.
 #
 # Use it instead of "! <command>". For example, when <command> dies due to a
@@ -560,7 +648,7 @@ test_expect_code() {
 	shift
 	"$@"
 	exit_code=$?
-	if test $exit_code = $want_code; then
+	if test "$exit_code" = "$want_code"; then
 		return 0
 	fi
 
@@ -570,7 +658,7 @@ test_expect_code() {
 
 # Public: Compare two files to see if expected output matches actual output.
 #
-# The TEST_CMP variable defines the command used for the comparision; it
+# The TEST_CMP variable defines the command used for the comparison; it
 # defaults to "diff -u". Only when the test script was started with --verbose,
 # will the command's output, the diff, be printed to the standard output.
 #
@@ -617,14 +705,14 @@ test_seq() {
 	while test "$i" -le "$j"
 	do
 		echo "$i" || return
-		i=$(expr "$i" + 1)
+		i=$(("$i" + 1))
 	done
 }
 
 # Public: Check if the file expected to be empty is indeed empty, and barfs
 # otherwise.
 #
-# $1 - File to check for emptyness.
+# $1 - File to check for emptiness.
 #
 # Returns 0 if file is empty, 1 otherwise.
 test_must_be_empty() {
@@ -636,6 +724,36 @@ test_must_be_empty() {
 	fi
 }
 
+# debugging-friendly alternatives to "test [-f|-d|-e]"
+# The commands test the existence or non-existence of $1. $2 can be
+# given to provide a more precise diagnosis.
+test_path_is_file () {
+	if ! test -f "$1"
+	then
+		echo "File $1 doesn't exist. $2"
+		false
+	fi
+}
+
+test_path_is_dir () {
+	if ! test -d "$1"
+	then
+		echo "Directory $1 doesn't exist. $2"
+		false
+	fi
+}
+
+# Check if the directory exists and is empty as expected, barf otherwise.
+test_dir_is_empty () {
+	test_path_is_dir "$1" &&
+	if test -n "$(find "$1" -mindepth 1 -maxdepth 1)"
+	then
+		echo "Directory '$1' is not empty, it contains:"
+		ls -la "$1"
+		return 1
+	fi
+}
+
 # Public: Schedule cleanup commands to be run unconditionally at the end of a
 # test.
 #
@@ -723,7 +841,7 @@ test_done() {
 		say_color warn "# still have $test_broken known breakage(s)"
 	fi
 	if test "$test_broken" != 0 || test "$test_fixed" != 0; then
-		test_remaining=$(( $test_count - $test_broken - $test_fixed ))
+		test_remaining=$((test_count - test_broken - test_fixed))
 		msg="remaining $test_remaining test(s)"
 	else
 		test_remaining=$test_count
@@ -760,20 +878,15 @@ test_done() {
 	esac
 }
 
-# Public: Root directory containing tests. Tests can override this variable,
-# e.g. for testing Sharness itself.
-: ${SHARNESS_TEST_DIRECTORY:=$(pwd)}
-export SHARNESS_TEST_DIRECTORY
-
 # Public: Source directory of test code and sharness library.
 # This directory may be different from the directory in which tests are
 # being run.
-: ${SHARNESS_TEST_SRCDIR:=$(cd $(dirname $0) && pwd)}
+: "${SHARNESS_TEST_SRCDIR:=$(cd "$(dirname "$0")" && pwd)}"
 export SHARNESS_TEST_SRCDIR
 
 # Public: Build directory that will be added to PATH. By default, it is set to
 # the parent directory of SHARNESS_TEST_DIRECTORY.
-: ${SHARNESS_BUILD_DIRECTORY:="$SHARNESS_TEST_DIRECTORY/.."}
+: "${SHARNESS_BUILD_DIRECTORY:="$SHARNESS_TEST_DIRECTORY/.."}"
 PATH="$SHARNESS_BUILD_DIRECTORY:$PATH"
 export PATH SHARNESS_BUILD_DIRECTORY