test_that("single_quote works", {
  expect_identical(single_quote(character()), character())
  expect_identical(single_quote(NA), NA_character_)
  expect_identical(single_quote(""), "''")
  expect_identical(single_quote(1:5), c("'1'", "'2'", "'3'", "'4'", "'5'"))
})

test_that("double_quote works", {
  expect_identical(double_quote(character()), character())
  expect_identical(double_quote(NA), NA_character_)
  expect_identical(double_quote(""), '""')
  expect_identical(double_quote(1:5), c('"1"', '"2"', '"3"', '"4"', '"5"'))
})

test_that("backtick works", {
  expect_identical(backtick(character()), character())
  expect_identical(backtick(NA), NA_character_)
  expect_identical(backtick(""), '``')
  expect_identical(backtick(1:5), c("`1`", "`2`", "`3`", "`4`", "`5`"))
})
