test_that("pd_stack() works", {
  # three days
  expect_warning(
    dd <- prism_archive_subset(
      "ppt", 
      "daily", 
      mon = 1, 
      years = 1981:2011, 
      resolution = '4km'
    )
  )
  expect_s4_class(x <- pd_stack(dd), "RasterStack")
  expect_equal(dim(x)[3], length(dd))
  expect_setequal(names(x), dd)
  
  # 2 months
  expect_warning(
    mm <- prism_archive_subset(
      "tdmean", "monthly", years = 2005, resolution = '4km'
    )
  )
  expect_s4_class(x <- pd_stack(mm), "RasterStack")
  expect_equal(dim(x)[3], length(mm))
  expect_setequal(names(x), mm)
  
  # combo month and days
  cc <- c(dd, mm)
  expect_s4_class(x <- pd_stack(cc), "RasterStack")
  expect_equal(dim(x)[3], length(cc))
  expect_setequal(names(x), cc)
})