Bah. Looks like another dependency dropping support for Node 16 although this one seems to be unintentional. In particular: chai depends on assertion-error, which uses deno bundle to compile TS to JS, which generates code using static class initialization blocks, which node 16 doesn't support. However, both chai and assertion-error claim to support node >= 12. Based on the overall tenor of the JS/node community, I kind of assume that if I brought this to their attention they would wontfix it and change the stated compatibility versions.
Copying from #2154: