Log message:
(devel/R-testthat) Fix build, two DEPENDS+ were missing

Log message:
(devel/R-testthat) Add TEST_DEPENDS+=  R-devtools

Log message:
(devel/R-testthat) Updated 2.2.1 to 2.3.1

# testthat 2.3.1

* The last version of testthat introduced a performance regression in
  error assertions (#963). To fix it, you need to install rlang 0.4.2.

* Fixed error assertions with rJava errors (#964).

* Fixed issue where error and warning messages were not retrieved with
  `conditionMessage()` under certain circumstances.

# testthat 2.3.0

## Conditions

This release mostly focusses on an overhaul of how testthat works with \ 
conditions (i.e. errors, warnings and messages). There are relatively few \ 
user-facing changes, although you should now see more informative backtraces \ 
from errors and failures.

* Unexpected errors are now printed with a simplified backtrace.

* `expect_error()` and `expect_condition()` now display a backtrace
  when the error doesn't conform to expectations (#729).

* `expect_error()`, `expect_warning()` and `expect_message()` now call
  `conditionMessage()` to get the condition message. This generic
  makes it possible to generate messages at print-time rather than
  signal-time.

* `expect_error()` gets a better warning message when you test for a custom
  error class with `regexp`.

* New `exp_signal()` function is a condition signaller that
  implements the testthat protocol (signal with `stop()` if the
  expectation is broken, with a `continue_test` restart).

* Existence of restarts is first checked before invokation. This makes
  it possible to signal warnings or messages with a different
  condition signaller (#874).

* `ListReporter` now tracks expectations and errors, even when they occur
  outside of tests. This ensures that `stop_on_failure` matches the results
  displayed by the reporter (#936).

* You can silence warnings about untested error classes by
  implementing a method for `is_uninformative_warning()`. This method
  should be lazily registered, e.g. with `vctrs::s3_register()`. This
  is useful for introducing an experimental error class without
  encouraging users to depend on the class in their tests.

* Respect options(warn = -1) to ignore all warnings (@jeroen #958).

## Expectations

* Expectations can now be explicitly subclassed with
  `new_expectation()`. This constructor follows our new conventions
  for S3 classes and takes an optional subclass and optional
  attributes.

* Unquoted inputs no longer potentially generate multiple test messages (#929).

* `verify_output()` no longer uses quasiquotation, which fixes issues
  when verifying the output of tidy eval functions (#945).

* `verify_output()` gains a `unicode` parameter to turn on or off the
  use of Unicode characters by the cli package. It is disabled by
  default to prevent the tests from failing on platforms like Windows
  that don't support UTF-8 (which could be your contributors' or your
  CI machines).

* `verify_output()` now correctly handles multi-line condition
  messages.

* `verify_output()` now adds spacing after condition messages,
  consistent with the spacing added after normal output.

* `verify_output()` has a new syntax for inserting headers in output
  files: insert a `"# Header"` string (starting with `#` as in
  Markdown) to add a header to a set of outputs.

## Other minor improvements and bug fixes

* `compare.numeric()` uses a more sophisticated default tolerance that will
  automatically skip tests that rely on numeric tolerance if long doubles are
  not available (#940).

* `JunitReporter` now reports tests in ISO 8601 in the UTC timezone and
  uses the maximum precision of 3 decimal places (#923).

Log message:
Add a missing dependency on devel/R-R6.