core: shutdown Blockchain gracefully in tests

pkg/core/blockchain_test.go

@@ -15,6 +15,7 @@ import (
 
 func TestAddHeaders(t *testing.T) {
 	bc := newTestChain(t)
+	defer bc.Close()
 	lastBlock := bc.topBlock.Load().(*block.Block)
 	h1 := newBlock(bc.config, 1, lastBlock.Hash()).Header()
 	h2 := newBlock(bc.config, 2, h1.Hash()).Header()

pkg/core/gas_price_test.go

@@ -14,6 +14,7 @@ import (
 // https://github.com/neo-project/neo/blob/master-2.x/neo.UnitTests/UT_InteropPrices.cs#L245
 func TestGetPrice(t *testing.T) {
 	bc := newTestChain(t)
+	defer bc.Close()
 	systemInterop := bc.newInteropContext(trigger.Application, storage.NewMemoryStore(), nil, nil)
 
 	v := bc.spawnVMWithInterops(systemInterop)