如何为 ggplot 图编写测试 [英] How to write a test for a ggplot plot

问题描述

我有很多生成绘图的函数，通常使用 ggplot2.现在，我正在生成绘图并测试基础数据.但我想知道是否有合理的方法来测试该图是否包含我期望的图层/选项或图形元素是否符合预期.

I have a lot of functions that generate plots, typically with ggplot2. Right now, I'm generating the plot and testing the underlying data. But I'd like to know if there's a reasonable way to test that the plot contains the layers/options I expect it to or that graphical elements match expectations.

例如:

library(ggplot2)
library(scales) # for percent()
library(testthat)

df <- data.frame(
  Response = LETTERS[1:5],
  Proportion = c(0.1,0.2,0.1,0.2,0.4)
)

#' @export plot_fun
plot_fun <- function(df) {
  p1 <- ggplot(df, aes(Response, Proportion)) +
    geom_bar(stat='identity') + 
    scale_y_continuous(labels = percent)
return(p1)
}

test_that("Plot returns ggplot object",{
  p <- plot_fun(df)
  expect_is(p,"ggplot")
})

test_that("Plot uses correct data", {
  p <- plot_fun(df)
  expect_that(df, equals(p$data))

})

这是我被卡住的地方

test_that("Plot layers match expectations",{
  p <- plot_fun(df)
  expect_that(...,...)
})

test_that("Scale is labelled percent",{
  p <- plot_fun(df)
  expect_that(...,...)
})

也许有更直接的方法?

推荐答案

这似乎就是您的目标，尽管对绘图参数和内容的具体要求当然会有所不同.但是对于您在上面精心制作的示例，这些测试都应该通过:

This seems to be what you're aiming at, though specific requirements for plotting parameters and contents will vary of course. But for the example you nicely crafted above these tests should all pass:

##  Load the proto library for accessing sub-components of the ggplot2
##    plot objects:
library(proto)

test_that("Plot layers match expectations",{
  p <- plot_fun(df)
  expect_is(p$layers[[1]], "proto")
  expect_identical(p$layers[[1]]$geom$objname, "bar")
  expect_identical(p$layers[[1]]$stat$objname, "identity")
})

test_that("Scale is labelled 'Proportion'",{
  p <- plot_fun(df)
  expect_identical(p$labels$y, "Proportion")
})

test_that("Scale range is NULL",{
  p <- plot_fun(df)
  expect_null(p$scales$scales[[1]]$range$range)
})

这个问题和它的答案为描述ggplot对象的其他方法提供了一个很好的起点，以防您有其他想要测试的东西.

This question and its answers offer a good starting point on other ways to characterize ggplot objects in case you have other things you'd like to test.

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