To provide a reference to how the tester works with a real 100% IBM CGA card
and monitor, a Full-D1 MPEG-2 video of some of the more demanding tests in an earlier version of the program is available courtesy of The Internet Archive. It is
highly recommended to watch the video before attempting to use the tester, so
that you can have an idea of what some of the more demanding tests are supposed to look like. (The video is somewhat outdated as it doesn't cover all of the tests present in the current version, but it covers the more important ones.)
Here is a streaming version of that video, for the curious:
A VOGONS thread where someone runs the tester against many VGA cards in their CGA compatibility modes and records the results.
CGACAL is a program that displays a simple color chart, and the webpage has an image of what that chart is supposed to look like. There is also an explanation of why color index #6 is generated as dark yellow but shows up on the monitor as brown, something that has caused a lot of confusion for emulator authors.