test(plus): add tests

sh/tests/plus_test.sh

@@ -0,0 +1,24 @@
+#!/bin/bash
+
+set -euo pipefail
+IFS='
+'
+
+script_dirS=$(cd -P "$(dirname "$BASH_SOURCE")" &>/dev/null && pwd)
+
+challenge() {
+    submitted=$(bash "$script_dirS"/student/plus.sh $1 $2)
+    expected=$(bash "$script_dirS"/solutions/plus.sh $1 $2)
+
+    diff <(echo "$submitted") <(echo "$expected")
+}
+
+challenge "1" "2"
+challenge "4" "2"
+challenge "3" "-3"
+challenge "0" "0"
+challenge "2" "-3"
+challenge "-4" "1"
+challenge "-2" "-1"
+challenge "10" "-5"
+challenge "-11" "20"