Add tests and development environment

[katauber]

Add tests and a development environment with hot reload.
Resolves #3

[fsteeg]

Great, hot reloading and testing works.

Some details / remarks:

• I've tweaked the README to make the testing steps more explicit in 79bd7e9.
• I've inlined some variables and extracted a getCompletionItems method in the tests in 8c11178.
• To me it feels like the tests have a lot of redundancy in their description strings. For instance, I think I'd skip the DisplayName annotations, IMO seeing the method names is fine, and avoids having to keep them in sync. I feel similar about the traditional-style assertions, e.g. assertNotNull & "should return a non-null". I think assertj-style assertions avoid a lot of that redundancy and read better, see e.g. in lobid-gnd-ui.
• Should we perhaps link to the playground CONTRIBUTING.md instead of duplicating it here?

[katauber]

Great, hot reloading and testing works.

Some details / remarks:

• I've tweaked the README to make the testing steps more explicit in 79bd7e9.
• I've inlined some variables and extracted a getCompletionItems method in the tests in 8c11178.

Thank you

• To me it feels like the tests have a lot of redundancy in their description strings. For instance, I think I'd skip the DisplayName annotations, IMO seeing the method names is fine, and avoids having to keep them in sync. I feel similar about the traditional-style assertions, e.g. assertNotNull & "should return a non-null". I think assertj-style assertions avoid a lot of that redundancy and read better, see e.g. in lobid-gnd-ui.

Looking at the code this may have redundancies but what I like about the display names is how it looks when running gradlew test:

instead of

The strings in the assert parts are not really necessary. I will remove that.

• Should we perhaps link to the playground CONTRIBUTING.md instead of duplicating it here?

I'm not sure about that. On one hand there sure will be changes in the CONtributing.md that apply to both repositories. On the other hand I like that e.g. links for creating a new issue fit the corresponding repository (https://github.com/metafacture/metafacture-lsp/issues/new). I also made some changes like
Describe the exact steps which reproduce the problem in as many details as possible. For example, start by explaining which client you used to connect to a language server. When listing steps, don't just say what you did, but explain how you did it. For example, if you send a request, explain what your call looks like and how you send it to the server. because the example of the playground didn' fit here.

[fsteeg]

+1

[katauber]

Deployed, call websocket via wss://test.metafacture.org/ls