test_that("operators work", {
  o <- function(x) x[order(x[, 1], x[, 2]), ]

  g1 <- make_ring(10)
  g2 <- make_star(11, center = 11, mode = "undirected")
  gu <- union(g1, g2)
  expect_that(vcount(gu), equals(11))
  expect_that(ecount(gu), equals(20))
  expect_that(
    o(rbind(as_edgelist(g1), as_edgelist(g2))),
    equals(o(as_edgelist(gu)))
  )

  gdu <- disjoint_union(g1, g2)
  expect_that(
    o(as_edgelist(gdu)),
    equals(o(rbind(
      as_edgelist(g1),
      as_edgelist(g2) + vcount(g1)
    )))
  )

  ####

  expect_true(graph.isomorphic(difference(gu, g1), g2))

  ####

  expect_true(graph.isomorphic(intersection(gu, g2), g2))

  expect_true(graph.isomorphic(
    intersection(gu, g1,
      keep.all.vertices = FALSE
    ),
    g1
  ))

  ####

  x <- complementer(complementer(g2))
  expect_true(identical_graphs(x, g2))

  ####

  gc <- compose(gu, g1)
  expect_that(vcount(gc), equals(11))
  expect_that(ecount(gc), equals(60))
  expect_that(diameter(gc), equals(2))
})

test_that("Union of directed named graphs", {
  graphs <- list(
    make_graph(~ 1:2:3:4:5, 1 -+ 2, 1 -+ 3, 2 -+ 3, 2 -+ 4, 3 -+ 4, 1 -+ 5, 3 -+ 5),
    make_graph(~ 1:2:3:4:5, 2 -+ 3, 1 -+ 4, 2 -+ 4, 3 -+ 4, 2 -+ 5, 3 -+ 5),
    make_graph(~ 1:2:3:4:5, 1 -+ 2, 1 -+ 3, 2 -+ 4, 3 -+ 4, 1 -+ 5, 4 -+ 5)
  )

  gg <- union.igraph(graphs)

  expect_equal(vcount(gg), 5)
  expect_equal(ecount(gg), 10)
})

test_that("edge reversal works", {
  # directed graph
  g <- make_graph(~ 1 -+ 2, 1 -+ 3, 1 -+ 4, 2 -+ 3, 3 -+ 4)
  g2 <- reverse_edges(g, 1:3)
  expected <- make_graph(~ 1 +- 2, 1 +- 3, 1 +- 4, 2 -+ 3, 3 -+ 4)
  expect_true(isomorphic(g2, expected))

  # undirected graph
  g <- make_graph(~ 1 -- 2, 1 -- 3, 1 -- 4, 2 -- 3, 3 -- 4)
  g2 <- reverse_edges(g, 1:3)
  expect_true(identical_graphs(g, g2))

  # all edges
  g <- make_graph(~ 1 -+ 2, 1 -+ 3, 1 -+ 4, 2 -+ 3, 3 -+ 4)
  g2 <- reverse_edges(g)
  expect_that(vcount(g2), equals(vcount(g)))
  expect_that(as_edgelist(g2), equals(as_edgelist(g)[, c(2, 1)]))

  # graph with isolated vertices
  g <- make_graph(~ 1:2:3:4:5, 1 -+ 2, 1 -+ 4)
  g2 <- reverse_edges(g)
  expect_that(vcount(g2), equals(vcount(g)))
  expect_that(as_edgelist(g2), equals(as_edgelist(g)[, c(2, 1)]))
})

test_that("t() is aliased to edge reversal for graphs", {
  g <- make_graph(~ 1 -+ 2, 1 -+ 3, 1 -+ 4, 2 -+ 3, 3 -+ 4)
  expect_that(vcount(t(g)), equals(vcount(g)))
  expect_that(as_edgelist(t(g)), equals(as_edgelist(g)[, c(2, 1)]))
})