test_dir() does not set TESTTHAT_PKG env var

[jennybc]

devtools::test() calls testthat::test_dir(), which doesn't set the TESTTHAT_PKG env var. I get this failure using devtools::test() on testthat itself:

✖ |  12 1     | test_dir [0.1 s]
─────────────────────────────────────────────────────────────
test-test_dir.R:12: failure: TESTHAT_PKG env var set to the package being tested
testing_package() not equal to "testthat".
1/1 mismatches
x[1]: ""
y[1]: "testthat"

[lionel-]

We also need this for the new deprecation tools, so we can check that the caller inherits from the namespace of the package being tested and only warn then.

[lionel-]

Thanks!