Alpha/Tests/delegation: add double registration test

Emptied and then recredited between the two self-delegations.

src/proto_alpha/lib_protocol/test/delegation.ml

@@ -882,7 +882,7 @@ let valid_delegate_registration_switch_delegation_credit_debit amount () =
   Assert.equal_pkh ~loc:__LOC__ orig_delegate delegate_pkh
 
 (** C- a second self-delegation should raise an `Active_delegate` error *)
-(* with implicit contract with some credits *)
+(* with implicit contract with some credit *)
 let double_registration () =
   Context.init 1 >>=? fun (b, bootstrap_contracts) ->
   Incremental.begin_construction b >>=? fun i ->
@@ -932,6 +932,37 @@ let double_registration_when_empty () =
       | Delegate_storage.Active_delegate -> true
       | _ -> false)
 
+(* with implicit contract emptied then recredited after first self-delegation  *)
+let double_registration_when_recredited () =
+  Context.init 1 >>=? fun (b, bootstrap_contracts) ->
+  Incremental.begin_construction b >>=? fun i ->
+  let bootstrap = List.hd bootstrap_contracts in
+  let account = Account.new_account () in
+  let pkh = Account.(account.pkh) in
+  let impl_contract = Contract.implicit_contract pkh in
+  (* credit 1μꜩ+ check balance *)
+  Op.transaction (I i) bootstrap impl_contract Tez.one_mutez >>=? fun create_contract ->
+  Incremental.add_operation i create_contract >>=? fun i ->
+  Assert.balance_is ~loc:__LOC__ (I i) impl_contract Tez.one_mutez >>=? fun _ ->
+  (* self delegation *)
+  Op.delegation (I i) impl_contract (Some pkh) >>=? fun self_delegation ->
+  Incremental.add_operation i self_delegation >>=? fun i ->
+  (* empty the delegate account *)
+  Op.transaction (I i) impl_contract bootstrap Tez.one_mutez >>=? fun empty_contract ->
+  Incremental.add_operation i empty_contract >>=? fun i ->
+  Assert.balance_is ~loc:__LOC__ (I i) impl_contract Tez.zero >>=? fun _ ->
+  (* credit 1μꜩ+ check balance *)
+  Op.transaction (I i) bootstrap impl_contract Tez.one_mutez >>=? fun create_contract ->
+  Incremental.add_operation i create_contract >>=? fun i ->
+  Assert.balance_is ~loc:__LOC__ (I i) impl_contract Tez.one_mutez >>=? fun _ ->
+  (* second self-delegation *)
+  Op.delegation (I i) impl_contract (Some pkh) >>=? fun second_registration ->
+  Incremental.add_operation i second_registration >>= fun err ->
+
+  Assert.proto_error ~loc:__LOC__ err (function
+      | Delegate_storage.Active_delegate -> true
+      | _ -> false)
+
 let tests_delegate_registration =
   [
     (*** unregistered delegate key: no self-delegation ***)
@@ -1012,6 +1043,7 @@ let tests_delegate_registration =
     (*** double registration ***)
     Test.tztest "double registration" `Quick double_registration ;
     Test.tztest "double registration when delegate account is emptied" `Quick double_registration_when_empty ;
+    Test.tztest "double registration when delegate account is emptied and then recredited" `Quick double_registration_when_recredited ;
   ]