(v1.6.0.9023) new unit test flow

tests/testthat.R

@@ -26,8 +26,7 @@
 # the testthat package is in Suggests, but very old R versions will not be
 # able to install it. Yet, we want basic R CMD CHECK's in those R versions 
 # as well, so only run unit tests in later R versions:
-if (require("testthat")) {
-  library(testthat, warn.conflicts = FALSE)
+if (require("testthat", warn.conflicts = FALSE)) {
   library(AMR)
   test_check("AMR")
 }