test_that("basicDistance returns dat and cost", {
  dat <- data.frame(x1 = 1:6, x2 = rnorm(6), z = c(1, 1, 0, 0, 0, 0), prc = rep(1L, 6))
  out <- basicDistance(dat)
  expect_type(out, "list")
  expect_named(out, c("dat", "cost"))
  expect_s3_class(out$dat, "data.frame")
  expect_true(is.matrix(out$cost) || inherits(out$cost, "matrix"))
  expect_true(all(c("id", "z", "prc") %in% names(out$dat)))
  expect_equal(nrow(out$dat), 6L)
  n_t <- sum(dat$z == 1)
  n_c <- sum(dat$z == 0)
  expect_equal(nrow(out$cost), n_t)
  expect_equal(ncol(out$cost), n_c)
  rn <- as.numeric(rownames(out$cost))
  cn <- as.numeric(colnames(out$cost))
  expect_equal(sort(rn), sort(out$dat$id[out$dat$z == 1]))
  expect_equal(sort(cn), sort(out$dat$id[out$dat$z == 0]))
})

test_that("basicDistance relabels conflicting id column", {
  dat <- data.frame(id = 1:4, z = c(1, 1, 0, 0), prc = 1L, w = 1:4)
  out <- suppressWarnings(basicDistance(dat))
  expect_true("id" %in% names(out$dat))
  expect_true(any(grepl("^Previous", names(out$dat))))
})

test_that("basicDistance requires z and prc columns", {
  expect_error(basicDistance(data.frame(x = 1:3)), "z must be a column")
  expect_error(basicDistance(data.frame(x = 1:3, z = 1:3)), "prc must be a column")
})

test_that("basicDistance rejects invalid z", {
  dat <- data.frame(x = 1:3, z = c(1, 2, 0), prc = 1:3)
  expect_error(basicDistance(dat))
})

test_that("basicDistance with compute_distance FALSE returns dat and NULL cost", {
  dat <- data.frame(x1 = 1:4, x2 = rnorm(4), z = c(1, 1, 0, 0), prc = rep(1L, 4))
  out <- basicDistance(dat, compute_distance = FALSE)
  expect_named(out, c("dat", "cost"))
  expect_null(out$cost)
  expect_true(all(c("id", "z", "prc") %in% names(out$dat)))
  expect_equal(nrow(out$dat), 4L)
})

test_that("basicDistance requires at least one treated and one control", {
  dat <- data.frame(x = 1:3, z = c(1, 1, 1), prc = 1:3)
  expect_error(basicDistance(dat), "at least one treated")
  dat$z <- c(0, 0, 0)
  expect_error(basicDistance(dat), "at least one treated")
})

test_that("basicDistance accepts logical z (coerced to numeric)", {
  dat <- data.frame(x = 1:4, z = c(TRUE, TRUE, FALSE, FALSE), prc = rep(1L, 4))
  out <- basicDistance(dat)
  expect_equal(out$dat$z, c(1, 1, 0, 0))
})

test_that(".validate_cost rejects wrong cost dimensions or names", {
  dat <- basicDistance(data.frame(x = 1:4, z = c(1, 1, 0, 0), prc = rep(1L, 4)))$dat
  cost_ok <- matrix(1:4, 2, 2, dimnames = list(c("1", "2"), c("3", "4")))
  expect_true(blockDesign:::.validate_cost(cost_ok, dat))
  cost_bad_dim <- matrix(1, 1, 2, dimnames = list("1", c("3", "4")))
  expect_error(blockDesign:::.validate_cost(cost_bad_dim, dat), "nrow")
  cost_bad_names <- matrix(1:4, 2, 2, dimnames = list(c("1", "2"), c("3", "9")))
  expect_error(blockDesign:::.validate_cost(cost_bad_names, dat), "match")
})