Revert "Don't run any tests"

This reverts commit c2e0d9a.

Author: lorenzwalthert

tests/testthat.R

@@ -1,8 +1,8 @@
-# library(testthat)
-# library(styler)
-# test_check("styler") # checks multiple files, in parallel
-#
-# # checks file one by one, not parallel
-# Sys.setenv(STYLER_TEST_IS_TRULY_PARALLEL = FALSE)
-# test_file("testthat/test-cache-high-level-api.R")
-# test_file("testthat/tests-cache-require-serial.R")
+library(testthat)
+library(styler)
+test_check("styler") # checks multiple files, in parallel
+
+# checks file one by one, not parallel
+Sys.setenv(STYLER_TEST_IS_TRULY_PARALLEL = FALSE)
+test_file("testthat/test-cache-high-level-api.R")
+test_file("testthat/tests-cache-require-serial.R")