Implement unit testing

[rsubtil]

Unit testing will massively help in ensuring no internal behavior breaks, and it can be used to test many scenarios, such as saving game data, scraping, setting configurations, etc...

Frameworks available: gut and GdUnit3

[rsubtil]

One good use case for unit testing is ensuring UI focus scenarios don't break randomly, which is something that constantly does.

Therefore this now takes some priority, thus it no longer belongs in the backlog. Like previously said, GUT and gdUnit4 seem to be the big ones right now, so which one to use should be investigated and pondered now.

[rsubtil]

As there's two prominent frameworks, and unit testing is crucial to ensure good UX, I'll be testing the workflow on both and grading them in different categories:

General

• Activity (is being maintained?)
• Support (open for bug reports? support channels available?)
• Documentation (complete? tutorials? advanced features?)
• CI integration (easy to integrate? works in headless mode?)

  Code

• Ease of writing tests
• Reusable functions/components for boilerplate setup

  UI

• Injection of input actions (actions? keyboard? controller?)
• Focus changes (can detect current focus? change focus?)
• Scene loading (can unit test scene files? node structure?)
• Other (TTS?)

[rsubtil]

After testing both GUT and gdUnit4, here are some notes I've gathered:

General

• Activity (is being maintained?): Both are being actively maintained.
• Support (open for bug reports? support channels available?): Both seem to show great support and openness for communication and bug reports.
• Documentation (complete? tutorials? advanced features?): Both have great documentation
• CI integration (easy to integrate? works in headless mode?): gdUnit4 has a slightly more straightforward CLI interface

  Unit tests

• Ease of writing tests: Both are very similar in unit test workflow. Readibility wise, gdUnit4 follows a more strictly typed approach, thus it's easier to read what a given test is testing for.
• Reusable functions/components for boilerplate setup: Both offer setup/teardown routines, and allow extending base classes for common functionality. GUT allows for inner classes, which makes for more contained unit test files when compared to gdUnit4.

  Integration tests

• Scene loading (can unit test scene files? node structure?): While both offer unit testing of scene files, gdUnit4 was easier to setup and has better wrappers for this scenario.
• Injection of input actions (actions? keyboard? controller?): Both can inject input actions easily. GUT supports actions, while gdUnit4 only supports raw key/mouse input events.
• Focus changes (can detect current focus? change focus?): Both can fetch nodes and focus information.

There isn't much difference in feature-set, but gdUnit4 has some QoL decisions that I like, so we'll use this one.