Easier testing of base graphics

[richierocks]

You can write code to draw base plots in several ways. For example, the following are all equivalent.

plot(cars$speed, cars$dist)

plot(dist ~ speed, cars)

with(cars, plot(speed, dist))

library(magrittr)
cars %$% plot(speed, dist)

Writing SCTs to check for all syntaxes is tricky. You have to do something like this:

test_or({
  ex() %>% check_function('plot') %>% {
    check_arg(., 'x') %>% check_equal()
    check_arg(., 'y') %>% check_equal()
  }
}, {
  ex() %>% override_solution('plot(dist ~ speed, cars))') %>% check_function('plot') %>% {
    check_arg(., 'formula') %>% check_equal()
    check_arg(., 'data') %>% check_equal()
  }
}, {
  ex() %>% override_solution('with(cars, plot(speed, dist))') %>% check_function('with') %>% {
    check_arg(., 'data') %>% check_equal()
    check_arg(., 'expr') %>% check_function('plot') %>% {
      check_arg(., 'x') %>% check_equal(eval = FALSE)
      check_arg(., 'y') %>% check_equal(eval = FALSE)
    }
  }
}, {
  ex() %>% override_solution('cars %$% plot(speed, dist)') %>%  {
    check_code(., 'cars %$%', fixed = TRUE)
    check_function(., 'plot') %>% {
      check_arg(., 'x') %>% check_equal(eval = FALSE)
      check_arg(., 'y') %>% check_equal(eval = FALSE)
    }
  }
})

Ideally, there would be a test_base_plot() function that handled all the specific cases.

One complication is that formula syntax is not supported for all base plot types. For example, hist() doesn't allow this. So you'd need a completely separate test_base_hist().

It might be easier from a technical point of view if the plot was first converted to a grid plot, in order to have an object to test. You can do this using grid.echo() and grid.grab() from the gridGraphics package.

See https://journal.r-project.org/archive/2015-1/murrell.pdf

FYI For base plotting, the Data Visualization in R course has longer, messy SCTs for the different cases in Ch1 and Ch2 (I didn’t get round to doing them for the later chapters yet) https://github.com/datacamp/courses-data-vis-in-r