Skip tests with testthat if not available

Author: llrs-roche

tests/testthat.R

@@ -1,2 +1,5 @@
-library(testthat)
-test_check("rtables", reporter = "check")
+if (requireNamespace("testthat", quietly = TRUE)) {
+  library(testthat)
+  library(rtables)
+  test_check("rtables", reporter = "check")
+}