With GPG=/usr/local/bin/gpg (master as of rG243f9176e799: gpg: New command --quick-revoke-sig), I invoked:
while export GNUPGHOME=$(mktemp -d) && $GPG --batch --passphrase '' --quick-gen-key "test <t@gniibe.org>" ed25519 && $GPG -o e.gpg --export-secret-key test && rm $GNUPGHOME/private-keys-v1.d/* && $GPG --import e.gpg; do rm e.gpg; date; done
... and it shows an error soon like:
gpg: key 045AB2BF3812ABE9: 1 bad signature gpg: key 045AB2BF3812ABE9: no valid user IDs gpg: this may be caused by a missing self-signature