test_that("add_edges keeps edge id order", {
  g <- make_empty_graph(10)
  edges <- c(1, 2, 2, 3, 3, 4, 1, 6, 1, 7, 9, 10)
  g2 <- add_edges(g, edges)
  ec <- ecount(g2)
  ec2 <- length(edges) / 2
  expect_equal(ec, ec2)
  expect_equal(get.edge.ids(g2, edges), seq_len(length(edges) / 2))
})

test_that("add_edges adds attributes", {
  g <- make_empty_graph(10)
  g3 <- add_edges(g, (edges <- c(1, 5, 2, 6, 3, 10, 4, 5)),
    attr = list(weight = (weights <- c(1, 2, 1, -1)))
  )
  expect_that(ecount(g3), equals(length(edges) / 2))
  expect_that(get.edge.ids(g3, edges), equals(seq_len(length(edges) / 2)))
  expect_that(E(g3)$weight, equals(weights))
})

test_that("add_edges unknown attributes to NA", {
  g <- make_empty_graph(10)
  g2 <- add_edges(g, (edges <- c(1, 2, 2, 3, 3, 4, 1, 6, 1, 7, 9, 10)))
  g4 <- add_edges(g2, c(1, 4, 4, 6, 7, 1), attr = list(weight = c(-1, 1, -2.5)))
  expect_true(all(is.na(E(g4)$weight[seq_len(length(edges) / 2)])))
})

test_that("add_edges appends attributes properly", {
  g <- make_empty_graph(10)
  g3 <- add_edges(g, (edges1 <- c(1, 5, 2, 6, 3, 10, 4, 5)),
    attr = list(weight = (weights1 <- c(1, 2, 1, -1)))
  )
  g5 <- add_edges(g3, (edges2 <- c(10, 9, 10, 10, 1, 1)),
    attr = list(weight = (weights2 <- c(100, 100, 100)))
  )
  expect_that(E(g5)$weight, equals(c(weights1, weights2)))
})

test_that("add_edges signals error for zero vertex ids", {
  g <- make_full_graph(5) %du% make_full_graph(5) %du% make_full_graph(5)
  expect_that(
    add_edges(g, c(0, 5, 0, 10, 5, 10)),
    throws_error("Invalid vertex")
  )
})