test_that("season returns correct season for valid Date input", {
  expect_equal(season(as.Date("2025-01-15")), factor("Winter"))
  expect_equal(season(as.Date("2025-05-10")), factor("Spring"))
  expect_equal(season(as.Date("2025-07-01")), factor("Summer"))
  expect_equal(season(as.Date("2025-10-15")), factor("Fall"))
})

test_that("season returns correct season for valid POSIXct input", {
  expect_equal(season(as.POSIXct("2025-01-15 12:00:00")), factor("Winter"))
  expect_equal(season(as.POSIXct("2025-04-25 08:00:00")), factor("Spring"))
  expect_equal(season(as.POSIXct("2025-08-01 18:00:00")), factor("Summer"))
  expect_equal(season(as.POSIXct("2025-09-30 00:00:00")), factor("Fall"))
})

test_that("season returns errors for non-dates and Undetermined for NA/NULL input", {
  expect_error(
    season("2025-01-15"),
    regexp = "input_date.*must be of class.*date, date-time"
  )
  expect_error(
    season(20250115),
    regexp = "input_date.*must be of class.*date, date-time"
  )
  expect_equal(
    season(NULL),
    expected = factor("Undetermined")
  )
})

test_that("season handles NA input correctly", {
  expect_error(season(NA))
})

test_that("season handles edge cases for months", {
  expect_equal(season(as.Date("2025-12-01")), factor("Winter"))
  expect_equal(season(as.POSIXct("2025-03-01 00:00:00")), factor("Spring"))
})