Make test output less verbose (#497)

Make output of `devtools::test()` less verbose so we focus on key information.

tests/testthat/test-unclean_column_names.R

@@ -1,4 +1,4 @@
-library(dplyr)
+library(dplyr, warn.conflicts = FALSE)
 
 test_that("reverses the effect of janitor::clean_names", {
   data <- tibble(x.x = 1, y = 1, z.z = 1)

tests/testthat/test-write_csv_file.R

@@ -1,7 +1,13 @@
 test_that("with readr < 1.4.0 and named argument `file` throws no error", {
-  skip_if(utils::packageVersion("readr") >= "1.4.0")
+  # Avoid verbose message of `skip_if()`
+  if (!utils::packageVersion("readr") >= "1.4.0") {
+    x <- tibble::tibble(x = 1)
+    file <- tempfile()
 
-  x <- tibble::tibble(x = 1)
-  file <- tempfile()
-  expect_error(write_csv_file(x = x, file = file), NA)
+    none <- NA
+    expect_error(write_csv_file(x = x, file = file), none)
+  }
+
+  # Avoid message "Reason: empty test"
+  expect_true(TRUE)
 })