The Ahem font was developed by Todd Fahrner to help test writers develop predictable tests. The font's em square is exactly square. Its ascent and descent is exactly the size of the em square. This means that the font's extent is exactly the same as its line-height, meaning that it can be exactly aligned with padding, borders, margins, and so forth.
The font's alphabetic baseline is 0.2em above its bottom, and 0.8em below its top. The font has an x-height of 0.8em.

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These fonts were created to support the testing of the font features in CSS, and are required to run some of the tests for those features.
The fonts are modified versions of Gentium Basic, licensed by SIL under the Open Font License which allows modifications as long as the terms of the license are met.
The original fonts were used to create the family 'CSSTest Basic'. This family has four faces and can be used for testing bold / italics. A subsetted version of this font with only glyphs for basic ASCII characters is 'CSSTest ASCII'. This was used to make the other variations. Most of the modications are to the name table and character maps, for the most part glyphs were not modified.
The fonts are available for download both individually and as a ZIP package below.
The files test.html and test.xhtml test that the fonts have been correctly installed.

The fonts in this folder are all test fonts from https://github.com/simoncozens/test-fonts , which are licensed as:
Copyright 2019 Simon Cozens. All rights reserved. Licensed under the Apache License, Version 2.0 (the “License”);
They're all test fonts, with CBDT having only 'A' glyph, the rest of the color fonts both A & B, and the baseline test only having L and 道, and an ideographic and roman baseline.