dat <- tibble::tribble(
  ~air, ~wind, ~water, ~month,
  -99,    NA,  23,     1,
  -98,    NA,  NA,     1,
  25,     30,  21,     2,
  NA,     99,  NA,     2,
  23,     40,  NA,     2
)

test_that("miss_var_table errors on NULL",{
  expect_snapshot(
    error = TRUE,
    miss_var_table(NULL)
    )
})
test_that("miss_var_table errors when a non-dataframe given", {
  expect_snapshot(
    error = TRUE,
    miss_var_table(1)
  )
  expect_snapshot(
    error = TRUE,
    miss_var_table("a")
  )
  expect_snapshot(
    error = TRUE,
    miss_var_table(matrix(0))
  )
})

test_that("miss_var_table produces a tibble", {
  expect_s3_class(miss_var_table(dat), "tbl_df")
})

aq_group <- dplyr::group_by(dat, month)

test_that("miss_var_table grouped_df returns a tibble", {
  expect_s3_class(miss_var_table(aq_group), "tbl_df")
})

test_that("grouped_df returns 1 more column than regular miss_var_table", {
  expect_equal(ncol(miss_var_table(aq_group)),
               ncol(miss_var_table(dat))+1)
})

test_that("grouped_df returns a column named 'Month'", {
  expect_identical(names(miss_var_table(aq_group)),
                   c("month", "n_miss_in_var", "n_vars","pct_vars"))
})

test_that("grouped_df returns a dataframe with more rows than regular", {
  expect_gt(nrow(miss_var_table(aq_group)),
            nrow(miss_var_table(dat)))
})

test_that("grouped_df returns a column named 'Month' with the right levels", {
  expect_identical(unique(miss_var_table(aq_group)$month),
                   c(1,2))
})