diff --git a/tester/run-tests.sh b/tester/run-tests.sh
index a3b0a8a..0f1dd82 100755
--- a/tester/run-tests.sh
+++ b/tester/run-tests.sh
@@ -1,6 +1,6 @@
 #! /usr/bin/env bash
 
-# run_test test_number
+# run_test testnumber
 run_test () {
     testfile=tests/$1.run
     # cat $testfile
@@ -8,7 +8,7 @@ run_test () {
     return 0
 }
 
-# check_test test_number out/err
+# check_test testnumber out/err
 check_test () {
     outdiff=$(diff tests/$1.$2 tests-out/$1.$2)
     outerr=$?
@@ -23,20 +23,78 @@ check_test () {
     return 0
 }
 
+# run_and_check testnumber printerror
+#   testnumber: the test to run and check
+#   printerrer: if 1, print an error if test does not exist
+run_and_check () {
+    if [[ ! -f tests/$1.run ]]; then
+	if (( $2 == 1 )); then
+	    echo "test $1 does not exist" >&2; exit 1
+	fi
+	exit 0
+    fi
+    run_test $1
+    check_test $1 out
+    check_test $1 err
+    builtin echo -e "\e[32mtest $1: passed\e[0m"
+    return 0
+}
+
+# usage: call when args not parsed, or when help needed
+usage () {
+    echo "usage: run-tests.sh [-h] [-v] [-t test]"
+    return 0
+}
+
+#
+# main program
+#
+verbose=0
+specific=""
+
+while true; do
+    case "$1" in
+    -h)
+	usage
+	exit 0
+        ;;
+    -v)
+        verbose=1
+        ;;
+    -t)
+        shift;
+	if (( $# == 0 )); then
+	    usage
+	    echo "-t needs a specific test number" >&2; exit 1
+	fi
+        specific=$1
+	number='^[0-9]+$'
+	if ! [[ $specific =~ $number ]]; then
+	    usage
+	    echo "-t must be followed by a number" >&2; exit 1
+	fi
+        ;;
+    esac
+    shift
+    if (( $# == 0 )); then
+	break
+    fi
+done
+
 if [[ ! -d tests-out ]]; then
     mkdir tests-out
 fi
 
-(( testnum = 1 ))
+# run just one test
+if [[ $specific != "" ]]; then
+    run_and_check $specific 1
+    exit 0
+fi
 
+# run all tests
+(( testnum = 1 ))
 while true; do
-    if [[ ! -f tests/$testnum.run ]]; then
-	exit 0
-    fi
-    run_test $testnum
-    check_test $testnum out
-    check_test $testnum err
-    builtin echo -e "\e[32mtest $testnum: passed\e[0m"
+    run_and_check $testnum 0
     (( testnum = $testnum + 1 ))
 done