Review comments

runtime/src/runtime.rs

@@ -108,13 +108,7 @@ fn execute_instruction(
         program_accounts,
         tick_height,
     )
-    .map_err(|err| match err {
-        ProgramError::CustomError(mut error) => {
-            error.truncate(32);
-            ProgramError::CustomError(error)
-        }
-        e => e,
-    })?;
+    .map_err(verify_error)?;
 
     // Verify the instruction
     for ((pre_program_id, pre_lamports, pre_userdata), post_account) in
@@ -233,6 +227,16 @@ where
     Ok(())
 }
 
+fn verify_error(err: ProgramError) -> ProgramError {
+    match err {
+        ProgramError::CustomError(mut error) => {
+            error.truncate(32);
+            ProgramError::CustomError(error)
+        }
+        e => e,
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -312,4 +316,18 @@ mod tests {
         );
     }
 
+    #[test]
+    fn test_verify_error() {
+        let short_error = ProgramError::CustomError(vec![1, 2, 3]);
+        let expected_short_error = short_error.clone(); // short CustomError errors should be untouched
+        assert_eq!(verify_error(short_error), expected_short_error);
+
+        let long_error = ProgramError::CustomError(vec![8; 40]);
+        let expected_long_error = ProgramError::CustomError(vec![8; 32]); // long CustomError errors should be truncated
+        assert_eq!(verify_error(long_error), expected_long_error);
+
+        let other_error = ProgramError::GenericError;
+        let expected_other_error = other_error.clone(); // non-CustomError errors should be untouched
+        assert_eq!(verify_error(other_error), expected_other_error);
+    }
 }