Snapshot testing for whole files
Whole file snapshot testing is designed for testing objects that don't have
a convenient textual representation, with initial support for images
(.png, .jpg, .svg), data frames (.csv), and text files
(.R, .txt, .json, ...).
The first time expect_snapshot_file() is run, it will create
_snaps/{test}/{name}.{ext} containing reference output. Future runs will
be compared to this reference: if different, the test will fail and the new
results will be saved in _snaps/{test}/{name}.new.{ext}. To review
failures, call snapshot_review().
We generally expect this function to be used via a wrapper that takes care of ensuring that output is as reproducible as possible, e.g. automatically skipping tests where it's known that images can't be reproduced exactly.
expect_snapshot_file(path, name = basename(path), binary = TRUE, cran = FALSE)
path |
Path to file to snapshot. |
name |
Snapshot name, taken from |
binary |
If |
cran |
Should these expectations be verified on CRAN? By default, they are not, because snapshot tests tend to be fragile because they often rely on minor details of dependencies. |
# To use expect_snapshot_file() you'll typically need to start by writing
# a helper function that creates a file from your code, returning a path
save_png <- function(code, width = 400, height = 400) {
path <- tempfile(fileext = ".png")
png(path, width = width, height = height)
on.exit(dev.off())
code
path
}
path <- save_png(plot(1:5))
path
## Not run:
expect_snapshot_file(save_png(hist(mtcars$mpg)), "plot.png")
## End(Not run)
# You'd then also provide a helper that skips tests where you can't
# be sure of producing exactly the same output
expect_snapshot_plot <- function(name, code) {
# Other packages might affect results
skip_if_not_installed("ggplot2", "2.0.0")
# Or maybe the output is different on some operation systems
skip_on_os("windows")
# You'll need to carefully think about and experiment with these skips
path <- save_png(code)
expect_snapshot_file(path, paste0(name, ".png"))
}Please choose more modern alternatives, such as Google Chrome or Mozilla Firefox.