Add unit test runner for autocompletion

[HolonProduction]

To prevent GDScript changes from breaking auto completion capabilities.

This PR adds the possibility to write Auto Completion tests. However it does not add any tests. I want to have the runner merged before working on test cases.

[HolonProduction]

Just noticed that there is no Github CI that runs tests with mono enabled. Would this be possible? I see no reliable way to test auto completion with SCRIPT types without using another script language besides GDScript. Because any way of obtaining a SCRIPT typed reference to a GDScript might break if we decide to intelligently upgrade the type in the future.

[AThousandShips]

This is because of issues, see the workflow file comment:

Disabled due freeze caused by mix Mono build and CI

[AThousandShips]

I've tested running a few times with the tests enabled and don't see any freezing, but I think this should be enabled and tested extensively in a separate PR to avoid any problems, see here for the original reason

[HolonProduction]

This should be ready for a first round of review now, since I added the features which I wanted to add.

What still remains to do:

• squash the commits (will do at the end, but while in review having the history might be helpful)
• remove dummy tests (will do at the end, but they are needed for testing)

[AThousandShips]

LGTM, seems to pass tests and the tests makes sense to me

[vnen]

The idea itself looks good to me, I just found some small details.

I also wonder if we can have an easy way to create the cfg files since writing them by hand might be tricky and prone to typos, especially if they get big (though tests should probably be small anyway).

[vnen]

This 0xFFFF character might be annoying to add as there is no an easy way to insert it besides copying and pasting, and it's inconsistent how it's shown across editors. Though I can't think of a better alternative for this at the moment.

[HolonProduction]

We could choose some UTF8 emoji and replace it with 0xFFFF. The use of this emoji in the test would just be banned. Maybe ➡️ or 🖱️. But I'm not sure whether there could be problems because those emojis are longer then normal characters.

[HolonProduction]

I ended up using ➡. It doesn't solve the need for copy and pasting, but it should be correctly displayed by most editors.

Edit: I also thought about → or ⇒ since, at least on some systems they can be entered through the compose key (e.g. mine 😄). But some editors display ->/=> in the same (or a very similar) way. So I think it might get too confusing.

[vnen]

Thanks for working on this, BTW. It is something on my mind for a while so I'm glad to have tests for completion.

[HolonProduction]

I also wonder if we can have an easy way to create the cfg files since writing them by hand might be tricky and prone to typos, especially if they get big (though tests should probably be small anyway).

Generating them through CLI like the other GDScript test would be quite inconvenient I think. It sounds more like an entry for the tools menu which gives you some UI that allows to configure the test and spits out the cfg and maybe also the script with the inserted sentinel char. But since it would be dev only, having it in the menu seems wrong.

Maybe I will write a little editor plugin for it, but that is something to think about when actually writing test cases. I can also imagine that copy and pasting an existing cfg will be quite sufficient for most cases.

[vnen]

LGTM

[akien-mga]

Thanks!