test_that("calc_grass_age works", {
  expect_equal(
    calc_grass_age(
      ID = c(1, 1, 1, 1, "A"),
      B_LU_BRP = c(265, 265, 1079, 1079, 1079)
    ),
    expected = c(2, 1,0,0,0),
    tolerance = 0.1
  )
  expect_equal(
    calc_grass_age(
      ID = c(1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, "A"),
      B_LU_BRP = c(265, 265, 1079, 1079, 1079, 237,237, 265, 265, 265, 308, 308, 265)
    ),
    expected = c(2, 1,0,0,0,0,0,3,2,1,0,0,1),
    tolerance = 0.1
  )
})