Stricter checks for proper usage

tests/cpp.sh

@@ -61,10 +61,19 @@ if [ $# -eq 0 ]; then
 	exit $?
 fi
 
-while [ $# -gt 0 ]; do
+if [ $# -eq 1 -a -n "$output" ]; then
 	target="$1"
-	output="${target%.cpp}.o"
-	shift
 
 	LD_LIBRARY_PATH="../src" $CPP "$target" > "$output"
-done
+elif [ $# -gt 1 -a -z "$output" ]; then
+	while [ $# -gt 0 ]; do
+		target="$1"
+		output="${target%.cpp}.o"
+		shift
+
+		LD_LIBRARY_PATH="../src" $CPP "$target" > "$output"
+	done
+else
+	_usage
+	exit $?
+fi