Cover all Editor implementations with tests

[nicoespeon]

I had decided not to write integration tests because I couldn't make Jest work with vscode-api.

It means that changes made to the VSCodeEditor implementation should be manually tested. It's OK because it doesn't change very often.

But as I'm implemented a VueVSCodeEditor now, I have the same problem. I've been thinking about it, and I have 2 solutions in mind:

1. Try again to get Jest & vscode-api work together. Last try was in May 2019 so things might have improved here.
2. Otherwise, wrap vscode-api in a Facade that I can inject to VSCode editors. I will be able to Subclass & Override it in tests, so I could apply the existing contract tests to VSCodeEditor and VueVSCodeEditor. This will bring more code in the "Domain" part of Abracadabra and leave very simple code in the Infrastructure part, which is desirable if I can't test my Editor implementations in integration.

I finally managed to get Jest & mocha working together, so no need for both scenario described above.

What would scenario 2 have looked like?

What we have now

What we will have after

class VSCodeEditor implements Editor {
  constructor(private vscodeApi: VSCodeAPI) {}
}

class VSCodeAPI {
  // Thin Facade on top of `vscode-api`
  // It just makes it easier to Subclass in tests (no need to hijack the import mechanism to mock)
}

And in tests:

class FakeVSCodeAPI extends VSCodeAPI {
  // Override methods so we can control read/write
  // Make it possible to test the logic of VSCodeEditor
  // VSCodeAPI logic will be left untested, until we can do integration tests
}

If we can do integration tests, this would still be interesting in making vscode-api upgrades easier. But not by much. It would be equally fine to test VSCodeEditor in integration because it's still small.

[nicoespeon]

Regarding the first option, here are interesting hints:

• https://code.visualstudio.com/api/working-with-extensions/testing-extension#the-test-script
• unable to import vscode in test using jest microsoft/vscode-test#37 (comment)
• Offer Jest as a testing solution for testing extensions microsoft/vscode-test#23

[nicoespeon]

Doing great, promising progress:

I could access VS Code API from within a test file, using mocha, without having conflicts with Jest unit tests that still exist in the project.

I need to polish the configuration & make everything easy to use, but I should have that ready very soon 🎉

[nicoespeon]

Got them running! Remaining tasks before calling it a day:

• Document how it works
• Get them run in CI (if possible, not sure about VS Code limitations about that)

[nicoespeon]

Done!

I updated the docs accordingly:

• New ADR => https://github.com/nicoespeon/abracadabra/blob/master/docs/adr/0010-integration-tests.md
• CONTRIBUTING guide => https://github.com/nicoespeon/abracadabra/blob/master/CONTRIBUTING.md#run-the-tests