Testwikidata is getting spambot hit, and pointlessly. We turned off direct account creations for wikimaniawiki (T247185) and it has been hugely effective for stopping the spambots.
Can I suggest that we should replicate that task as there is little need to create a SUL account at testwikidata. We can create a direction for the account creation back to wikidata, similar to what was done at
Accounts can be created at [[d:Special:CreateAccount|Wikidata:Create Account]].