Rust tests for var x and let x default to undefined

.gitignore

@@ -2,11 +2,15 @@
 .idea/
 *.iml
 
+# Vim
+.*.swp
+.*.swo
+
 # Build
 target
 dist
 **/*.rs.bk
 node_modules
 .DS_Store
 yarn-error.log
-.vscode/settings.json
+.vscode/settings.json

src/lib/exec.rs

@@ -630,3 +630,32 @@ impl Interpreter {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use crate::exec;
+
+    #[test]
+    fn empty_let_decl_undefined() {
+        let scenario = r#"
+        let a;
+        a == undefined;
+        "#;
+
+        let pass = String::from("true");
+
+        assert_eq!(exec(scenario), pass);
+    }
+
+    #[test]
+    fn empty_var_decl_undefined() {
+        let scenario = r#"
+        let b;
+        b == undefined;
+        "#;
+
+        let pass = String::from("true");
+
+        assert_eq!(exec(scenario), pass);
+    }
+}