test: add cd test without args

src/builtins/cd.rs

@@ -27,6 +27,11 @@ mod tests {
     use super::*;
     use std::path::Path;
 
+    #[test]
+    fn test_cd_no_args() {
+        assert_eq!(Cd.execute(&mut BuiltinConfig::new(), vec![]), Ok(()))
+    }
+
     #[test]
     fn test_cd_current() {
         assert_eq!(