test: add logout is builtin command test

src/builtins/mod.rs

@@ -96,6 +96,11 @@ mod tests {
         assert_eq!(is_builtin("help"), true);
     }
 
+    #[test]
+    fn test_is_builtin_logout(){
+        assert_eq!(is_builtin("logout"), true)
+    }
+
     #[test]
     fn test_is_builtin_ls() {
         assert_eq!(is_builtin("ls"), true);