Adds additional tests for the interface. Creates a new base test class
GodotXtermTest that adds some additional assert methods. Tests
inheriting from this should override the got_described_class() method.
Add instance of the described class named 'subject' will be created and
added to the scene tree before each test.
- Install Gut using gd-plug.
- Add some basic tests.
- Update workflow to run tests.
- Add test and gd-plug install/uninstall recipes to Justfile.
- Re-enable debug builds as these are used by editor when testing.
