The Unicode Text Rendering Reference System (UTRRS) is a open source web-based application which compares a rendered text character with a reference image of a text character, for comparison of differences between the two.
Comparing the results of a text rendering engine to actual text can be done without the ability to read or comprehend the language in question. This ability is available for Codepoints (Unicode Character Set), GSUB (Glyph Substitution), and GPOS (Glyph Positioning).