test(qmdb): add unit tests for StoreBatches type (#62)

* test(qmdb): add unit tests for StoreBatches type

Add comprehensive tests for the StoreBatches struct:
- new() and default() create empty batches
- is_empty() checks all batch types
- len() counts total operations across batches
- Deletion operations (None values)
- Debug implementation

* style: fix formatting in batch.rs tests

Author: refcell

crates/storage/qmdb/src/batch.rs

@@ -32,3 +32,83 @@ impl StoreBatches {
         self.accounts.len() + self.storage.len() + self.code.len()
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_new_creates_empty_batches() {
+        let batches = StoreBatches::new();
+        assert!(batches.is_empty());
+        assert_eq!(batches.len(), 0);
+    }
+
+    #[test]
+    fn test_default_creates_empty_batches() {
+        let batches = StoreBatches::default();
+        assert!(batches.is_empty());
+        assert_eq!(batches.len(), 0);
+    }
+
+    #[test]
+    fn test_is_empty_with_accounts() {
+        let mut batches = StoreBatches::new();
+        batches.accounts.push((Address::ZERO, Some([0u8; 80])));
+        assert!(!batches.is_empty());
+    }
+
+    #[test]
+    fn test_is_empty_with_storage() {
+        let mut batches = StoreBatches::new();
+        let key = StorageKey::new(Address::ZERO, 0, U256::ZERO);
+        batches.storage.push((key, Some(U256::from(100))));
+        assert!(!batches.is_empty());
+    }
+
+    #[test]
+    fn test_is_empty_with_code() {
+        let mut batches = StoreBatches::new();
+        batches.code.push((B256::ZERO, Some(vec![0x60, 0x00])));
+        assert!(!batches.is_empty());
+    }
+
+    #[test]
+    fn test_len_counts_all_operations() {
+        let mut batches = StoreBatches::new();
+
+        batches.accounts.push((Address::ZERO, Some([0u8; 80])));
+        batches.accounts.push((Address::repeat_byte(0x01), None));
+
+        let key1 = StorageKey::new(Address::ZERO, 0, U256::from(1));
+        let key2 = StorageKey::new(Address::ZERO, 0, U256::from(2));
+        let key3 = StorageKey::new(Address::ZERO, 0, U256::from(3));
+        batches.storage.push((key1, Some(U256::from(100))));
+        batches.storage.push((key2, Some(U256::from(200))));
+        batches.storage.push((key3, None));
+
+        batches.code.push((B256::ZERO, Some(vec![0x60, 0x00])));
+
+        assert_eq!(batches.len(), 6);
+    }
+
+    #[test]
+    fn test_deletion_operations() {
+        let mut batches = StoreBatches::new();
+
+        batches.accounts.push((Address::ZERO, None));
+        let key = StorageKey::new(Address::ZERO, 0, U256::ZERO);
+        batches.storage.push((key, None));
+        batches.code.push((B256::ZERO, None));
+
+        assert!(!batches.is_empty());
+        assert_eq!(batches.len(), 3);
+    }
+
+    #[test]
+    fn test_debug_impl() {
+        let batches = StoreBatches::new();
+        let debug_str = format!("{:?}", batches);
+        assert!(debug_str.contains("StoreBatches"));
+    }
+}