diff --git a/assert-extras.sh b/assert-extras.sh
new file mode 100644
index 0000000..b4f4769
--- /dev/null
+++ b/assert-extras.sh
@@ -0,0 +1,76 @@
+#!/usr/bin/env bash
+
+# assert-extras.sh 1.1 - supplementary bash unit testing functions
+# Note: This script should be sourced together with assert.sh,
+#       it is dependent on the functionality provided by that script.
+
+# assert_success <command> [stdin]
+assert_success() {
+	assert_raises "$1" 0 "${2:-}"
+}
+
+# assert_failure <command> [stdin]
+assert_failure() {
+    (( tests_ran++ )) || :
+    [[ -z "$DISCOVERONLY" ]] || return
+    status=0
+    (eval "$1" <<< ${2:-}) > /dev/null 2>&1 || status=$?
+    if [[ "$status" != "0" ]]; then
+        [[ -z "$DEBUG" ]] || echo -n .
+        return
+    fi
+    _assert_fail "program terminated with a zero return code; expecting non-zero return code" \
+    	"$1" "$2"
+}
+
+# assert_contains <command> <expected output...>
+assert_contains() {
+	_assert_with_grep '-F' "$@"
+}
+
+# assert_matches <command> <expected output...>
+assert_matches() {
+	_assert_with_grep '-E' "$@"
+}
+
+# assert_startswith <command> <expected start to stdout>
+assert_startswith() {
+	assert_success "[[ '$($1)' == '$2'* ]]"
+}
+
+# assert_endswith <command> <expected start to stdout>
+assert_endswith() {
+	assert_success "[[ '$($1)' == *'$2' ]]"
+}
+
+# _assert_with_grep <grep modifiers> <command> <expected output...>
+_assert_with_grep() {
+    local grep_modifier="$1"
+    local output="$($2)"
+    shift 2
+
+    while [ $# != 0 ]; do
+    	assert_raises "echo '$output' | $GREP $grep_modifier '$1'" 0 || return 1
+    	shift
+    done
+}
+
+# Returns the resolved command, preferring any gnu-versions of the cmd (prefixed with 'g') on
+# non-Linux systems such as Mac OS, and falling back to the standard version if not.
+_cmd() {
+	local cmd="$1"
+
+	local gnu_cmd="g$cmd"
+	local gnu_cmd_found=$(which "$gnu_cmd" 2> /dev/null)
+	if [ "$gnu_cmd_found" ]; then
+		echo "$gnu_cmd_found"
+	else
+		if [ "$(uname)" == 'Darwin' ]; then
+			echo "Warning: Cannot find gnu version of command '$cmd' ($gnu_cmd) on path." \
+			     "Falling back to standard command" >&2
+		fi
+		echo "cmd"
+	fi
+}
+
+GREP=$(_cmd grep)
diff --git a/assert.sh b/assert.sh
index ffd2b95..0b1d2d5 100644
--- a/assert.sh
+++ b/assert.sh
@@ -75,7 +75,7 @@ assert_end() {
     tests_endtime="$(date +%s%N)"
     # required visible decimal place for seconds (leading zeros if needed)
     local tests_time="$( \
-        printf "%010d" "$(( ${tests_endtime/%N/000000000} 
+        printf "%010d" "$(( ${tests_endtime/%N/000000000}
                             - ${tests_starttime/%N/000000000} ))")"  # in ns
     tests="$tests_ran ${*:+$* }tests"
     [[ -n "$DISCOVERONLY" ]] && echo "collected $tests." && _assert_reset && return
@@ -94,6 +94,8 @@ assert_end() {
         echo "$tests_failed of $tests failed$report_time."
     fi
     tests_failed_previous=$tests_failed
+    tests_ran_total=$(($tests_ran_total + $tests_ran))
+    tests_failed_total=$(($tests_failed_total + $tests_failed))
     [[ $tests_failed -gt 0 ]] && tests_suite_status=1
     _assert_reset
 }
@@ -103,7 +105,7 @@ assert() {
     (( tests_ran++ )) || :
     [[ -z "$DISCOVERONLY" ]] || return
     expected=$(echo -ne "${2:-}")
-    result="$(eval 2>/dev/null $1 <<< ${3:-})" || true
+    result="$(eval 2>/dev/null "$1" <<< ${3:-})" || true
     if [[ "$result" == "$expected" ]]; then
         [[ -z "$DEBUG" ]] || echo -n .
         return
@@ -119,7 +121,7 @@ assert_raises() {
     (( tests_ran++ )) || :
     [[ -z "$DISCOVERONLY" ]] || return
     status=0
-    (eval $1 <<< ${3:-}) > /dev/null 2>&1 || status=$?
+    (eval "$1" <<< ${3:-}) > /dev/null 2>&1 || status=$?
     expected=${2:-0}
     if [[ "$status" -eq "$expected" ]]; then
         [[ -z "$DEBUG" ]] || echo -n .
@@ -139,6 +141,7 @@ _assert_fail() {
     fi
     tests_errors[$tests_failed]="$report"
     (( tests_failed++ )) || :
+    return 1
 }
 
 skip_if() {
@@ -178,6 +181,8 @@ _skip() {
 
 _assert_reset
 : ${tests_suite_status:=0}  # remember if any of the tests failed so far
+: ${tests_ran_total:=0}     # remember the total number of tests ran (inc. failures)
+: ${tests_failed_total:=0}  # remember the total number of test failures
 _assert_cleanup() {
     local status=$?
     # modify exit code if it's not already non-zero
diff --git a/test-extras.sh b/test-extras.sh
new file mode 100755
index 0000000..3247264
--- /dev/null
+++ b/test-extras.sh
@@ -0,0 +1,122 @@
+#!/usr/bin/env bash
+
+source assert.sh
+source assert-extras.sh
+
+assert "echo foo" "foo"
+assert_raises "true" 0
+assert_raises "exit 127" 127
+
+assert_end sanity
+
+###
+### assert_success tests
+###
+
+# Tests expecting success
+assert_success "true"
+assert_success "echo foo"
+assert_success "cat" "foo"
+
+# Tests expecting failure
+assert_raises 'assert_success "false"' 1
+assert_raises 'assert_success "exit 1"' 1
+
+assert_end assert_success
+
+###
+### assert_failure tests
+###
+
+# Tests expecting success
+assert_failure "false"
+assert_failure "exit 1"
+assert_failure "exit -1"
+assert_failure "exit 42"
+assert_failure "exit -42"
+
+# Tests expecting failure
+assert_raises 'assert_failure "true"' 1
+assert_raises 'assert_failure "echo foo"' 1
+
+assert_end assert_failure
+
+###
+### assert_contains tests
+###
+
+# Tests expecting success
+assert_contains "echo foo" "foo"
+assert_contains "echo foobar" "foo"
+assert_contains "echo foo bar" "foo"
+assert_contains "echo foo bar" "bar"
+assert_contains "echo foo bar" "foo bar"
+
+# Tests expecting failure
+assert_failure 'assert_contains "echo foo" "foot"'
+assert_failure 'assert_contains "echo foo" "f.."'
+
+# Multi-word argument tests
+assert_contains "echo foo bar" "foo bar"
+assert_failure 'assert_contains "echo foo; echo bar" "foo bar"'
+
+# Multi-argument tests
+assert_contains "echo foo bar baz" "foo" "baz"
+assert_failure 'assert_contains "echo foo bar baz" "bar" "foo baz"'
+
+assert_end assert_contains
+
+###
+### assert_matches tests
+###
+
+# Tests expecting success
+assert_matches "echo foo" "f.."
+assert_matches "echo foobar" "f."
+assert_matches "echo foo bar" "^foo bar$"
+assert_matches "echo foo bar" "[az ]+"
+
+# Tests expecting failure
+assert_failure 'assert_matches "echo foot" "foo$"'
+
+# Multi-word argument tests
+assert_matches "echo foo bar" "foo .*"
+assert_failure 'assert_matches "echo foo; echo bar" "foo .*"'
+
+# Multi-argument tests
+assert_matches "echo foo bar baz" "^f.." "baz$"
+assert_failure 'assert_matches "echo foo bar baz" "bar" "foo baz"'
+
+assert_end assert_matches
+
+###
+### assert_startswith tests
+###
+
+# Tests expecting success
+assert_startswith "echo foo" "f"
+assert_startswith "echo foo" "foo"
+assert_startswith "echo foo; echo bar" "foo"
+
+# Tests expecting failure
+assert_failure 'assert_startswith "echo foo" "oo"'
+assert_failure 'assert_startswith "echo foo; echo bar" "foo bar"'
+assert_failure 'assert_startswith "echo foo" "."'
+
+assert_end assert_startswith
+
+###
+### assert_endswith tests
+###
+
+# Tests expecting success
+assert_endswith "echo foo" "oo"
+assert_endswith "echo foo" "foo"
+assert_endswith "echo foo; echo bar" "bar"
+
+# Tests expecting failure
+assert_failure 'assert_endswith "echo foo" "f"'
+assert_failure 'assert_endswith "echo foo; echo bar" "foo bar"'
+assert_failure 'assert_endswith "echo foo" "."'
+
+assert_end assert_endswith
\ No newline at end of file
diff --git a/tests.sh b/tests.sh
index e8c1425..c18b903 100755
--- a/tests.sh
+++ b/tests.sh
@@ -1,7 +1,5 @@
 #!/bin/bash
 
-set -e
-
 . assert.sh
 
 assert "echo"                           # no output expected
@@ -60,7 +58,7 @@ assert "_clean; skip_if false; assert_raises true; assert_end;" \
 assert "_clean; skip_if bash -c 'exit 1'; assert_raises false; assert_end;" \
 "all 0 tests passed."
 # subshells and pipes can be used in skip as well (albeit escaped)
-assert "_clean; skip_if 'cat /etc/passwd | grep \$(echo \$USER)';
+assert "_clean; skip_if 'id | grep \$(echo \$USER)';
 assert_raises false; assert_end;" \
 "all 0 tests passed."
 assert_end output
@@ -96,8 +94,9 @@ assert "_clean; x=0; assert 'x=1'; assert_raises 'x=2'; echo \$x" 0
 assert "_clean; x=0; assert 'export x=1'; assert_raises 'export x=2';
 echo \$x" 0
 # options do not leak
-assert_raises "set +e"
-assert_raises "shopt -o errexit"
+assert_raises "shopt -o errexit" 1
+assert_raises "set -e"
+assert_raises "shopt -o errexit" 1
 # skip properly resets all options
 assert_raises "_clean; set +e; skip; assert_raises false; shopt -o errexit" 1
 assert_raises "_clean; set -e; skip; assert_raises false; shopt -o errexit"
@@ -153,7 +152,8 @@ _date=22;
 assert_end" "all 1 tests passed in 2.000s."
 # commit: supported formatting codes
 assert "echo %s" "%s"
-assert "echo -n %s | wc -c" "2"
+# We trim the output from wc as the BSD version (on Mac OS) contains leading spaces
+assert "echo -n %s | wc -c | tr -d '[[:space:]]'" "2"
 # date with no nanosecond support
 date() {         # date mock
     echo "123N"
@@ -161,4 +161,9 @@ date() {         # date mock
 assert '_clean DEBUG=1 INVARIANT=; tests_starttime="0N"; assert_end' \
        '\nall 0 tests passed in 123.000s.'
 unset -f date  # bring back original date
+# commit: Supporting multiline inputs
+# We trim the output from wc as the BSD version (on Mac OS) contains leading spaces
+assert 'echo "this
+is a multiline echo" | wc -l | tr -d "[[:space:]]"' "2"
+assert 'echo -e "this\nis a multiline echo" | wc -l | tr -d "[[:space:]]"' "2"
 assert_end regression