WPT details: No, as it is tested at lower levels. Rendering tests exist internally, and could be added to WPT, but the CSS fonts spec does not mandate support for this specific font format so no strict assertions on format support can be made across browsers. Updated regression tests that test the variable functionality are continuously run on bots at the Skia golden master level, see the colrv1.cpp gm test there, based on a new variable test font released in the color-fonts repository. fonts/blob/main/fonts/test_glyphs-glyf_colr_1_variable.ttf This test font was used to compare rendering results between Chrome and FF and ensure interop.
COLRv1 color vector fonts have been released in Chrome 98 https://developer.chrome.com/blog/colrv1-fonts/ but this initial release supported only static functionality of the COLRv1 table. The COLRv1 specification defines integration with OpenType Variations which allows modifying font properties of gradients and transforms by means of changing variable axis parameters. This second step brings support for such variations to COLRv1.
This is a follow-up to the COLRv1 I2S https://groups.google.com/a/chromium.org/g/blink-dev/c/kDfj3rcA6sc/m/77Ary8NVBwAJ. The goal was and is to bring highly compact, expressive color vector fonts to the web with this next generation font format enabling powerful 2D graphics glyph definitions (gradients, transforms, compositing) and reuses existing contour definitions of the open font format OFF. This stage 2 of the COLRv1 release completes the full implementation of the specification by adding the variable functionality. Variable fonts are shipping in Chrome, which allows space efficient and expressive monochromatic fonts and is already used by Google Fonts and other font providers to increase efficiency in delivering web font families. COLRv1 fonts are shipping in Chrome, which bring compact, expressive and high performance color vector glyphs. Variable support for COLRv1 integrates variations with COLRv1 fonts and allows variability in COLRv1 fonts. This enables syncing and aligning gradient and transform parameters with variable shapes in the glyphs of the font. Imagine a variable color font with horizontal gradients in the stems of the letters: When the stem size changes, the gradient can align alongside the weight change of the font.
Samples: https://roettsch.es/var_colrv1.html