Improve desc_filter so you can select deeply nested tests

[kubajal]

Currently, desc_filter let's you:

• run either a single test_that or a single describe expressions and not an it expression
• run jest the top-level test_that and describe expressions

This PR expands desc_filter capabilities by adding support for:

• selecting it expressions
• selecting deeply nested describe expressions (and not only top-level) as per https://testthat.r-lib.org/reference/describe.html

This is implemented by making desc_filter accept list of test labels that act as selectors in the test hierarchy.

So e.g. running testthat::test_file("tests.R", desc=c("level 0, "level 1 A", "level 2 B"))

# tests.R
f()
describe("level 0", {
  g()
  describe("level 1", {
    h()
    it("level 2 A", {}),
    i()
    it("level 2 B", {})
    j()
})

effectively triggers just

f()
describe("level 0", {
  g()
  describe("level 1", {
    h()
    i()
    it("level 2 B", {})
})

This gives more room for good IDE integrations, e.g. fixing meakbiyik/vscode-r-test-adapter#24.

This PR is a continuation of #1904 and #1840.

[kubajal]

The error on Ubuntu is not related to my change and has been observed in other PRs too, e.g. #2061:

Error: Error: running the tests in ‘testthat.R’ failed
Error: Error: Failure in `/home/runner/work/_temp/package/testthat/testthat-tests/testthat.Rout.fail`
r ('test-local.R:38:3'): can override translation of error messages ─────
<notSubsettableError/error/condition>
Error in `mean[[1]]`: object of type 'closure' is not subsettable
Backtrace:

[kubajal]

@hadley could you have a look? This PR is ready for review.

[hadley]

@kubajal I'll take a look when I'm next working on testthat.

[hadley]

I'm not sure that this makes sense to me, given that there's often code run outside of it() blocks in describe(), so I don't think there's much guarantee that this will work in general, unfortunately.

[kubajal]

Perhaps my description was misleading. With my changes, any code outside of it(...) statement does get executed. It's just that the only it(...) statement that does get executed is the one with the provided desc argument.

Here are my 3 arguments to merge it:

• this PR will enable better IDE support for running just the failing assertions instead of running the whole suite of tests, e.g. in https://github.com/meakbiyik/vscode-r-test-adapter which I'm a contributor of and I would be interested in improving UX of testthat in VSCode
• the new code logic in this PR carefully mimics mechanism of selection of single describe() / testthat() statements but in a more granular way
• the changes still trigger the code run outside of it() statements

[kubajal]

@hadley could you please revisit this PR and the comment above?

[hadley]

In that case, I'd suggest:

• You make desc take a character vector rather than introducing an obscure new separator.
• You work on minimising the difference with the existing code so its easier for me to review.
• You include a test demonstrating the your code preserves other non-it() code blocks.

[kubajal]

Thanks, will fix that.

[kubajal]

@hadley the PR is ready for a new review.

I also updated the title and description of the PR so it is more precise.

[hadley]

Ok, I've reimplemented it in a way that's more easy for me to understand and refined all the tests.

@jennybc can you please take a look? This shouldn't change any existing behaviour but should enable recursive selection of tests inside other tests.

[hadley]

Fixes #2118