Need for non-UI end-to-end testing

[simark]

I recently wanted to make an end-to-end test involving Theia and clangd, to verify that some actions in the frontend (changing build configuration) worked correctly with clangd and that the system as a whole gave good results.

The only way right now is to do a UI test, where you simulate clicks in a Theia application. However, there is nothing in this test that inherently needs to be UI-driven. We only need some non-UI components of the frontend, a backend, and clangd.

I think it would be nice to be able to run tests where we instantiate some non-UI components of the frontend (including the bits necessary to connect to a backend) and drive the test from a standard mocha test file.

[svenefftinge]

Can't you just try to make it work and then we see how we can extract general parts if it's worth it?

[simark]

I tried a little bit and hit some road bumps, so I wanted to see if any of you saw any reason why this would be a bad idea, before going further.

[amiramw]

I did some integration non UI testings for the fontend modules of theia extensions (no backend modules).
In order to allow tests to access them I had to expose inversify internal dictionary by injecting the following code next to the initialization of the inversify container:

window.TheiaApiTest = {
    getServiceBindingByClass: (s) => {
        let filteredEntries = Array.from(container._bindingDictionary.getMap().entries())
            .filter(arr => arr[0].toString().startsWith("function " + s));
        let bindingPair = filteredEntries && filteredEntries[0];
        return bindingPair && bindingPair[1] && bindingPair[1][0] && bindingPair[1][0].cache;
    }
};

For my initial use case this method was enough but I guess that in time there will be more of them.

I used jest-puppeteer to execute code in the browser context in my tests. So the test code looks somewhat like this:

let value = await page.waitForFunction(() => {
      return TheiaApiTest.getServiceBindingByClass("MyContribution")
        .doSomething();
    });
expect(value).toEqual("hello");

If this mechanism is desired inside theia I can create a PR.

[paul-marechal]

@amiramw is it similar to #5654?

[amiramw]

As far as I understand yes. But I didn't get into it yet.

[vince-fugnitto]

Closed in #6852 :)