How do you unit test plugins? I have Codeception running on my local install without errors, but it's not yet actually doing anything. I am building several plugins and I can't figure out how you actually test a plugin? I have no app code at all, all functionality comes from the plugins.
I have seen other plugins running their own custom PhpUnit code inline, but shouldn't I be able to fire off Codeception from the root app and it will test available plugins?
Fully aware that this is a vague question, but I can't find any information about specifically testing Craft plugins.
Have you been through Craft's testing documentation? https://craftcms.com/docs/3.x/testing/
There's a pretty good walkthrough of the necessary steps there to test plugins: https://craftcms.com/docs/3.x/testing/testing-craft/setup.html
Or if you like more real-world examples, Commerce's tests are a good place to start: https://github.com/craftcms/commerce/blob/develop/codeception.yml
From then, you'd trigger all unit tests from the root of your project like:
./vendor/bin/codecept run unit

Or every test in a single file with:
./vendor/bin/codecept run tests/unit/helpers/LocaleHelperTest.php

Or a specific test within a single file with:
./vendor/bin/codecept run tests/unit/helpers/LocaleHelperTest.php:testEmailGetOrderLanguage