Integrate 'testthat' into the Tests feature for R packages

[jmcphers]

Currently, if you have an R package and open the Testing view, it says that 'No tests have been found in the workspace', even if the workspace contains testthat tests.

We should:

• Detect any testthat tests and display them in the Tests pane; support running tests, showing results, and jumping to errors
• Have a "Configure R Tests" button that helps new users set up testthat for the first time

[jennybc]

The first groundwork for this has been laid by @juliasilge in #915. That creates the scaffold for hooking into VS Code's test UI.

At the complete other extreme, I have standalone code that extracts the relevant test info (e.g. coordinates for test_that() calls, their descriptions) from a folder's worth of test files, using a tree-sitter-generated R parser. In a private repo: https://github.com/jennybc/treesitrrust.

The next phase is to create the plumbing that connects those two pieces.

Re: 'Have a "Configure R Tests" button that helps new users set up testthat for the first time'

☝️ if one can use R code, that is usethis::use_testthat() and, if not, then replicating that.

[jmcphers]

if one can use R code...

I think it's fine to lean on R code; it'd be nicer to have our own UI but not essential. We'll need an RStudio-like mechanism for helping users get bootstrapped by installing the packages needed for this kind of functionality ("configuring R tests requires usethis and testthat, would you like to install those now?").

[juliasilge]

With #1445 we can now run tests in a little self-contained R session or alternatively in the console.

[juliasilge]

With #915 merged in, we can now move on to a next step, such as parsing the test files.

[juliasilge]

In build 1214 I see:

• R package tests identified 🎉
• I can click to run a test 🎉
• the test does not run or return info to the UI about success/failure 😢

When I click to run a test, it looks like it is going but it never finishes (will wait for minutes) or returns success/failure info to the UI.

[jennybc]

Having experienced this myself now in build 1214, my leading hypothesis is that it's this, quoting @jmcphers:

One thing you'll need to watch out for when you get closer to making a PR is that it can be a little tricky to get wasm files to get picked up properly when the extension is webpacked for release. You'll probably have to add it to positron-r/positron.json.

It's clear (from logging) that the hang is at the test file parsing stage.

[jennybc]

Oh lordy, we're back in business and I think this is fixed now in release builds. A simple fix but rather hard to divine.

[juliasilge]

In build 1327, I can use the testing extension for R packages. Looking so great! 🎉

Passing tests:

A failing test: