EVM-IT: Test that nonces are increased even during balance queries.

testing/integration/tests/evm/features/SimpleCoin.feature

@@ -29,3 +29,14 @@ Feature: SimpleCoin
         | 5e969c4ac2f287128d6fd71e7d111dbd19a5b2bea59da5d5d908044a514f5f8e |
       When account 1 creates a SimpleCoin contract
       Then account 2 fails to create a SimpleCoin contract with 'Actor sequence invalid: 0 != 1'
+
+  Rule: Nonce increases
+
+    @wip
+    Scenario: Sending multiple messages to views, the tester and the state stay in sync
+      Given 1 random account
+      When account 1 creates a SimpleCoin contract
+      Then the balance of account 1 is 10000 coins
+      And the balance of account 1 is 10000 coins
+      And the balance of account 1 is 10000 coins
+      And the seqno of account 1 is 4

testing/integration/tests/fevm.rs

@@ -208,6 +208,11 @@ impl ContractTester {
         self.account_mut(acct).account.0
     }
 
+    /// Get the nonce of an account.`
+    pub fn account_seqno(&mut self, acct: &AccountNumber) -> u64 {
+        self.account_mut(acct).seqno
+    }
+
     /// Deploy a contract owned by an account.
     pub fn create_contract(
         &mut self,
@@ -282,13 +287,12 @@ impl ContractTester {
                 .expect("too much gas"),
         );
 
-        // I think the nonce doesn't need to increase for views. Need to check.
-        match call.function.state_mutability {
-            StateMutability::View | StateMutability::Pure => {}
-            _ => {
-                *self.account_mut(&acct) = account;
-            }
-        }
+        // I think the nonce doesn't need to increase for views, but
+        // maybe that's just an optimisation by actually using a local node.
+        // FWIW the system increases the seqno, it doesn't have a special
+        // relationship with the EVM actor.
+        // NB `call.function.state_mutability` would tell us.
+        *self.account_mut(&acct) = account;
 
         if !invoke_res.msg_receipt.exit_code.is_success() {
             return Err(ExecError {
@@ -343,6 +347,11 @@ macro_rules! contract_matchers {
                 .expect_err("contract creation should fail");
             assert!(format!("{err:?}").contains(&message))
         }
+
+        #[then(expr = "the seqno of {acct} is {int}")]
+        fn check_seqno(world: &mut $world, acct: $crate::AccountNumber, seqno: u64) {
+            assert_eq!(world.tester.account_seqno(&acct), seqno)
+        }
     };
 }