Add bash app, tests and run_tests file

tests/test_calculator.sh

@@ -0,0 +1,19 @@
+#!/bin/bash
+
+#incarca functia din aplicatie
+
+source ./app/calculator.sh
+
+echo "Test: add 2 + 3"
+
+result=$( add 2 3 )
+
+if [ "$result" -eq 5 ]; then
+echo "Test PASSED"
+exit 0
+
+else
+echo "Test FAILED"
+exit 1
+fi
+