Description of the change

This is a small simplification of our pre-test setup. Shouldn't change anything other than the number of moving parts.

For reference, this was originally introduced in #1402. Using callCommand instead of callProcess might always have been the better way to go; I don't know. But it seems to work well enough today.

Checklist:

• Added the change to the changelog's "Unreleased" section with a reference to this PR (e.g. "- Made a change (#0000)")
• Added myself to CONTRIBUTORS.md (if this is my first contribution)
• Linked any existing issues or proposals that this pull request should close
• Updated or added relevant documentation
• Added a test for the contribution (if applicable)