[Toybox] avoiding testing shell builtins

[Rob Landley]

On 6/22/19 11:26 AM, enh via Toybox wrote:
> i realized today that the kill tests are testing the shell's builtin
> kill, not the toybox kill. one solution would be to use env, but
> presumably that would be better in the infrastructure rather than
> having to remember to do it in each test that might be subverted by a
> builtin?

This is why I added testcmd and $C a while back. (Although currently it won't
work if the path to the testing directory has a space in it, because I hadn't
quoted $C. Just fixed that...)

Rob