expect_traces <- function(gg, n.traces, name) {
  stopifnot(is.numeric(n.traces))
  L <- expect_doppelganger_built(gg, paste0("density-", name))
  all.traces <- L$data
  no.data <- sapply(all.traces, function(tr) {
    is.null(tr[["x"]]) && is.null(tr[["y"]])
  })
  has.data <- all.traces[!no.data]
  expect_equivalent(length(has.data), n.traces)
  list(data=has.data, layout=L$layout)
}

# Draw a probability density estimation using geom_density
base <- ggplot(mtcars, aes(wt))

test_that("geom_density() is translated to area chart", {
  info <- expect_traces(base + geom_density(), 1, "simple")
  tr <- info$data[[1]]
  expect_identical(tr$type, "scatter")
  expect_identical(tr$mode, "lines")
  expect_identical(tr$fill, "toself")
})

test_that("geom_density() respects fill aesthetic", {
  gg <- base + geom_density(aes(fill = factor(vs)), alpha = 0.3)
  info <- expect_traces(gg, 2, "fill")
  trs <- info$data
  expect_identical(
    unique(sapply(trs, "[[", "type")), "scatter"
  )
  expect_identical(
    unique(sapply(trs, "[[", "fill")), "toself"
  )
  # check legend exists
  expect_true(info$layout$showlegend, TRUE)
  # check legend for each fill exists
  expect_true(all(sapply(trs, "[[", "showlegend")))
})

test_that("geom_density() respects colour aesthetic", {
  info <- expect_traces(base + geom_density(aes(colour=factor(vs))), 2, "color")
  trs <- info$data
  expect_identical(
    unique(sapply(trs, "[[", "type")), "scatter"
  )
  expect_identical(
    unique(sapply(trs, "[[", "fill")), "toself"
  )
})

g <- base + 
  geom_histogram(aes(y = after_stat(density)), binwidth = 0.5, fill = "pink") +
  geom_density(fill = "lightblue", alpha = 0.1)
  
test_that("geom_histogram(aes(y = after_stat(density))) + geom_density() works", {
  info <- expect_traces(g, 2, "histogram")
  trs <- info$data
  type <- unique(sapply(trs, "[[", "type"))
  expect_identical(sort(type), c("bar", "scatter"))
})

# Check if the traces are in the correct order when position = stack
# Generate ggplot object
p <- ggplot(data = mtcars, aes(x = mpg, fill = factor(cyl))) + 
  geom_density(position = "stack")

test_that("traces are ordered correctly in geom_density", {
  info <- expect_traces(p, 3, "traces_order")
  nms <- as.character(sapply(info$data, "[[", "name"))
  expect_identical(nms, c("4", "6", "8"))
})