Autocompletion bug for subcommands in zsh

on ZSH, the `hierarchy` test command always shows the top-level completions, even after a subcommand was selected.

Expected:
```
$ hierarchy sub2
-d           --directory  --num2       subsub1      subsub2
```

Actual:
```
$ hierarchy sub2
-h         --help     sub1       sub2       -V         --version
```