test_that("cluster_optimal works", {
  skip_if_no_glpk()

  g <- make_graph("Zachary")
  oc <- cluster_optimal(g)

  expect_that(
    as.vector(membership(oc)),
    equals(c(
      1, 1, 1, 1, 2, 2, 2, 1, 3, 3, 2, 1, 1, 1, 3, 3,
      2, 1, 3, 1, 3, 1, 3, 4, 4, 4, 3, 4, 4, 3, 3, 4,
      3, 3
    ))
  )
  expect_that(modularity(g, oc$membership), equals(oc$modularity))
  expect_that(length(oc), equals(4))
  expect_that(
    sizes(oc),
    equals(structure(c(11L, 5L, 12L, 6L),
      .Dim = 4L,
      .Dimnames = structure(
        list(`Community sizes` = c(
          "1", "2",
          "3", "4"
        )),
        .Names = "Community sizes"
      ),
      class = "table"
    ))
  )
})

test_that("weighted cluster_optimal works", {
  skip_if_no_glpk()

  local_rng_version("3.5.0")
  withr::local_seed(42)
  g <- make_full_graph(5) + make_ring(5)
  E(g)$weight <- sample(1:2, ecount(g), replace = TRUE)

  oc <- cluster_optimal(g)
  expect_that(modularity(oc), equals(0.4032))
})