test_that("cluster_optimal works", {
  skip_if_no_glpk()

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

  expect_equal(
    as.vector(membership(oc)),
    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_equal(modularity(g, oc$membership), oc$modularity)
  expect_equal(length(oc), 4)
  expect_equal(
    sizes(oc),
    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_equal(modularity(oc), 0.4032)
})