Set up automated bash tests with bats

[jotaen4tinypilot]

Resolves https://github.com/tiny-pilot/tinypilot/issues/1714. Related https://github.com/tiny-pilot/tinypilot/issues/1710. Stacked onto https://github.com/tiny-pilot/tinypilot/pull/1720.

This PR sets up bash tests with bats, and adds a first test suite for the strip-marker-sections script.

Notes

• Similar to how we do it with other test files, I put the .bats test file next to the script under test. The directive in .dockerignore removes it from the bundle / .deb file.
• The build_bash dev script is called “build” for consistency with build_python and build_javascript, even though we technically don’t build something. I’ve created https://github.com/tiny-pilot/tinypilot/issues/1716 for us to potentially reconsider this overall.
• In build_bash, it somehow felt reasonable to me to search all places that are likely to contain .bats files, even though we currently only have them in /opt/tinypilot-privileged/scripts/. I don’t feel strongly about this, though.
• For running the tests, there theoretically would be an official bats Docker image, however that doesn’t play nicely with our bash files: the docker image doesn’t have a symlink at /bin/bash, so it fails to execute any of our bash scripts that have a #!/bin/bash shebang (which is effectively all of them). We instead would either have to change all our shebangs to the (most portable) #!/usr/bin/env bash shebang, or we just install bats manually like done here (in the Circle conf).

[jotaen4tinypilot]

@jdeanwallace sorry for the PR/review flood… I’m not blocked by any of them, so no pressure from my side, especially if you want to play around a bit with bats.

[codeapprove[bot]]

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👀 @jotaen4tinypilot it's your turn, please take a look