mixed <- function() {
  d <- data.frame(variable = rep(c("wagt", "wrr"), each = 5),
                  obs = c(seq(9000, 17000, length.out = 5),
                          seq(4000, 9000, length.out = 5)),
                  stringsAsFactors = FALSE)
  d$pred <- d$obs * 1.05
  d
}

test_that("pooling statistics across variables warns", {
  expect_warning(gof("obs", "pred", data = mixed()), "more than one variable")
})

test_that("grouping by variable is accepted silently", {
  expect_silent(g <- gof("obs", "pred", data = mixed(), by = "variable"))
  expect_equal(nrow(g), 2L)
  expect_false(isTRUE(all.equal(g$rmse[1], g$rmse[2])))
})

test_that("a single variable never warns", {
  d <- mixed()[mixed()$variable == "wrr", ]
  expect_silent(gof("obs", "pred", data = d))
})

test_that("plot_one2one facets by variable rather than mixing units", {
  expect_message(plot_one2one(mixed()), "do not share units")
  p <- suppressMessages(plot_one2one(mixed()))
  expect_equal(nlevels(ggplot2::ggplot_build(p)$data[[1]]$PANEL), 2L)
})

test_that("an explicit facet is respected", {
  d <- mixed(); d$phase <- rep(c("Calibration", "Validation"), 5)
  expect_silent(p <- plot_one2one(d[d$variable == "wrr", ], facet = "phase"))
  expect_equal(nlevels(ggplot2::ggplot_build(p)$data[[1]]$PANEL), 2L)
})

test_that("per-variable statistics differ from the pooled figure", {
  g1 <- suppressWarnings(gof("obs", "pred", data = mixed()))
  g2 <- gof("obs", "pred", data = mixed(), by = "variable")
  # the pooled RMSE sits between the two, and its R2 is inflated
  expect_true(g1$rmse > min(g2$rmse) && g1$rmse < max(g2$rmse))
})