The data folder contains the results for screenshot tests. Screenshot tests make sure an icon looks the same as it did before a change to prevent regressions.
You can create one by simply using the test_screenshot proc.
This example test screenshots a red image and keeps it.
/// This is an example for screenshot tests, and a meta-test to make sure they work in the success case.
/// It creates a picture that is red on the left side, green on the other.
/datum/unit_test/screenshots/basic
/datum/unit_test/screenshots/basic/Run()
var/icon/red = icon('icons/blanks/32x32.dmi', "nothing")
red.Blend(COLOR_RED, ICON_OVERLAY)
test_screenshot("red", red)
Unfortunately, screenshot tests are sanest to test through a pull request directly, due to limitations with both DM and GitHub. | 