OSSubprocess works on macOS Mojave with 64-bit Pharo.

Load it the usual way:

Metacello new
  baseline: 'OSSubprocess';
  repository: 'github://pharo-contributions/OSSubprocess:master/repository';
  load.	

Run the tests. If Pharo was started like how applications are usually started on the Mac, by double-clicking the Pharo.app icon, Test Runner will report 40+ test errors.

Run Pharo the Unix way on the command line: ~/MyApps/Pharo.app/Contents/MacOS/Pharo mypharo7.image. Now all 114 tests pass. All 7 stress tests pass too. Tested with Pharo 7.0 pre-release image.