test_that("Error_LLH handles an all-root-node network correctly", {
  # A network with no edges: every node is a root node, exercising the
  # branch of Error_LLH that should report no error/mismatch terms.
  num.node <- 4
  SampleSize <- 50
  GeneData <- matrix(rbinom(num.node * SampleSize, 1, 0.5),
    nrow = num.node, ncol = SampleSize
  )
  TRFUM <- matrix(0, nrow = num.node, ncol = num.node)
  prior_para <- matrix(3, nrow = num.node + 1, ncol = 2)
  prior_para[num.node + 1, 1] <- 2
  prior_para[num.node + 1, 2] <- 100

  result <- Error_LLH(
    TRFUM = TRFUM, GeneData = GeneData, SampleSize = SampleSize,
    num.node = num.node, prior_para = prior_para, penalty = 0.1
  )

  expect_true(is.na(result[[1]][1])) # ErrorFactor: NA, no non-root nodes
  expect_true(is.na(result[[2]][num.node + 1])) # mismatch: NA
  expect_true(is.na(result[[2]][num.node + 2])) # Perror: NA

  log_post_model <- result[[1]][length(result[[1]])]
  expect_true(is.finite(log_post_model))
})