Rename helper function to firstCertificateIsNotRetirement.

This more accurately reflects the function's purpose.

We don't actually mind if the list of certificates is empty.

lib/core/test/unit/Cardano/Pool/DB/Arbitrary.hs

@@ -211,14 +211,14 @@ isValidSinglePoolCertificateSequence :: SinglePoolCertificateSequence -> Bool
 isValidSinglePoolCertificateSequence
  (SinglePoolCertificateSequence sharedPoolId certificates) =
  allCertificatesReferToSamePool &&
- firstCertificateIsRegistration
+ firstCertificateIsNotRetirement
  where
  allCertificatesReferToSamePool =
  all (== sharedPoolId) (getPoolCertificatePoolId <$> certificates)
- firstCertificateIsRegistration = case certificates of
+ firstCertificateIsNotRetirement = case certificates of
+ [] -> True
  Registration _ : _ -> True
- Retirement _ : _ -> False
- [] -> True
+ Retirement _ : _ -> False
 
 instance Arbitrary SinglePoolCertificateSequence where