expect_snapshot_ggplots: Visual snapshot test for ggplot2 plot(s)

Description

Renders ggplot2 objects to PNG with ragg and compares against a reference snapshot using expect_snapshot_doc().

When x is a list of ggplot2 objects, individual renderings are assembled into a single composite image via images_to_miniature(). By default each plot occupies its own row; use ncol to arrange several plots per row. The snapshot is always a single file named <name>.png, stored in testthat's _snaps directory.

If a plot fails to render, its slot is replaced by a blank white rectangle of the same dimensions, making the failure visible in the diff.

On the first run the reference snapshot is created and the test is reported as a new snapshot. Subsequent runs compare the current rendering against the stored reference.

Usage

expect_snapshot_ggplots(
  x,
  name,
  width = 9,
  height = 7,
  units = "in",
  res = 200,
  ncol = NULL,
  tolerance = 0.001
)

Value

The result of expect_snapshot_doc().

Arguments

x: a ggplot2 object or a list of ggplot2 objects.
name: a unique string used as the snapshot file name (<name>.png). Must be unique across the test file.
width, height: image dimensions (default 9 x 7 inches).
units: units for width/height, default "in".
res: resolution in DPI, default 200.
ncol: number of images per row in the composite when x is a list (default NULL, one image per row).
tolerance: ratio of different pixels allowed, default 0.001.