test_that("locf carries forward the last observed value", {
  x <- c(1, NA, NA, 4)
  expect_equal(locf(x), c(1, 1, 1, 4))
})

test_that("locf preserves leading NAs (nothing to carry forward)", {
  x <- c(NA, 2, NA, 4)
  expect_equal(locf(x), c(NA, 2, 2, 4))
})

test_that("locf handles multiple NA runs correctly", {
  x <- c(1, NA, NA, 4, NA, NA, 7)
  expect_equal(locf(x), c(1, 1, 1, 4, 4, 4, 7))
})

test_that("locf returns input unchanged when no NAs present", {
  x <- c(1, 2, 3, 4)
  expect_equal(locf(x), x)
})

test_that("locf returns all NAs when input is all NAs", {
  x <- rep(NA_real_, 5)
  expect_equal(locf(x), x)
})

test_that("locf preserves the class of the input (numeric)", {
  x <- c(1.5, NA, 3.5)
  expect_type(locf(x), "double")
})

test_that("locf handles NA followed immediately by a value", {
  x <- c(NA, 3, NA)
  expect_equal(locf(x), c(NA, 3, 3))
})

test_that("locf result has same length as input", {
  x <- c(1, NA, 3, NA, NA)
  expect_length(locf(x), length(x))
})