Added test

boa/src/exec/tests.rs

@@ -912,3 +912,23 @@ fn to_string() {
     assert_eq!(engine.to_string(&Value::rational(55.0)).unwrap(), "55");
     assert_eq!(engine.to_string(&Value::string("hello")).unwrap(), "hello");
 }
+
+#[test]
+fn calling_function_with_unspecified_arguments() {
+    let realm = Realm::create();
+    let mut engine = Interpreter::new(realm);
+    let scenario = r#"
+        function fibonacci(num, memo) {
+            memo = memo || {};
+
+            if (memo[num]) return memo[num];
+            if (num <= 1) return 1;
+
+            return memo[num] = fibonacci(num - 1, memo) + fibonacci(num - 2, memo);
+        }
+
+        fibonacci(1)
+    "#;
+
+    assert_eq!(forward(&mut engine, scenario), "1");
+}