fix: declare transaction error format

crates/blockifier/src/transaction/error_format_test.rs

@@ -1,3 +1,5 @@
+use starknet_api::core::ClassHash;
+use starknet_api::hash::StarkHash;
 use starknet_api::transaction::TransactionVersion;
 
 use crate::transaction::errors::TransactionExecutionError;
@@ -13,3 +15,15 @@ fn test_contract_class_version_mismatch() {
         "Declare transaction version 1 must have a contract class of Cairo version 2."
     );
 }
+
+#[test]
+fn test_declare_transaction_error_format() {
+    let error = TransactionExecutionError::DeclareTransactionError {
+        class_hash: ClassHash(StarkHash::THREE),
+    };
+    assert_eq!(
+        error.to_string(),
+        "Class with hash 0x0000000000000000000000000000000000000000000000000000000000000003 is \
+         already declared."
+    );
+}

crates/blockifier/src/transaction/errors.rs

@@ -59,7 +59,7 @@ pub enum TransactionExecutionError {
         String::from(gen_transaction_execution_error_trace(self))
     )]
     ContractConstructorExecutionFailed(#[from] ConstructorEntryPointExecutionError),
-    #[error("Class with hash {class_hash:?} is already declared.")]
+    #[error("Class with hash {:#064x} is already declared.", **class_hash)]
     DeclareTransactionError { class_hash: ClassHash },
     #[error(
         "Transaction execution has failed:\n{}",