init cache on restart (#3486)

substrate/core/client/db/src/light.rs

@@ -1030,26 +1030,37 @@ pub(crate) mod tests {
 
 	#[test]
 	fn cache_can_be_initialized_after_genesis_inserted() {
-		let db = LightStorage::<Block>::new_test();
+		let (genesis_hash, storage) = {
+			let db = LightStorage::<Block>::new_test();
 
-		// before cache is initialized => None
-		assert_eq!(db.cache().get_at(b"test", &BlockId::Number(0)), None);
+			// before cache is initialized => None
+			assert_eq!(db.cache().get_at(b"test", &BlockId::Number(0)), None);
 
-		// insert genesis block (no value for cache is provided)
-		let mut genesis_hash = None;
-		insert_block(&db, HashMap::new(), || {
-			let header = default_header(&Default::default(), 0);
-			genesis_hash = Some(header.hash());
-			header
-		});
+			// insert genesis block (no value for cache is provided)
+			let mut genesis_hash = None;
+			insert_block(&db, HashMap::new(), || {
+				let header = default_header(&Default::default(), 0);
+				genesis_hash = Some(header.hash());
+				header
+			});
 
-		// after genesis is inserted => None
-		assert_eq!(db.cache().get_at(b"test", &BlockId::Number(0)), None);
+			// after genesis is inserted => None
+			assert_eq!(db.cache().get_at(b"test", &BlockId::Number(0)), None);
 
-		// initialize cache
-		db.cache().initialize(b"test", vec![42]).unwrap();
+			// initialize cache
+			db.cache().initialize(b"test", vec![42]).unwrap();
 
-		// after genesis is inserted + cache is initialized => Some
+			// after genesis is inserted + cache is initialized => Some
+			assert_eq!(
+				db.cache().get_at(b"test", &BlockId::Number(0)),
+				Some(((0, genesis_hash.unwrap()), None, vec![42])),
+			);
+
+			(genesis_hash, db.db)
+		};
+
+		// restart && check that after restart value is read from the cache
+		let db = LightStorage::<Block>::from_kvdb(storage as Arc<_>).expect("failed to create test-db");
 		assert_eq!(
 			db.cache().get_at(b"test", &BlockId::Number(0)),
 			Some(((0, genesis_hash.unwrap()), None, vec![42])),