test command was supported since v3.2.0, see a8ffc31 (Add test command to run any unit test (#1092), 2023-07-28)
I hesitate to also add prepare command (see ./cmd/prepare.go@b43bd372) to completions, because it seems it’s no longer an everyday command. The default completion command created by cobra is also not added, see my topic on the Exercism Forum.