bug#29712: 26.0.90; Three emacs-26 elisp tests are failing on darwin

[Glenn Morris]

Alan Third wrote:

> If that's true I can think of two ways round it:
>
>   1. Create a temporary file and then check for its existence (e.g. in
>      /tmp).
>   2. Skip the test if the source directory doesn't exist.

3. Use a file that will exist, like doc-directory/DOC.

(Seems odd that none of the other tests using source-directory fail.)