Fix doc typo

Fixes #1843

Author: hadley

R/test-files.R

@@ -11,8 +11,8 @@
 #'
 #' @section Environments:
 #' Each test is run in a clean environment to keep tests as isolated as
-#' possible. For package tests, that environment that inherits from the
-#' package's namespace environment, so that tests can access internal functions
+#' possible. For package tests, that environment inherits from the package's
+#' namespace environment, so that tests can access internal functions
 #' and objects.
 #'
 #' @param path Path to directory containing tests.