accounts/abi/bind: support closing a simulated backend

accounts/abi/bind/backends/simulated.go

@@ -88,6 +88,12 @@ func NewSimulatedBackend(alloc core.GenesisAlloc, gasLimit uint64) *SimulatedBac
 	return NewSimulatedBackendWithDatabase(rawdb.NewMemoryDatabase(), alloc, gasLimit)
 }
 
+// Close terminates the underlying blockchain's update loop.
+func (b *SimulatedBackend) Close() error {
+	b.blockchain.Stop()
+	return nil
+}
+
 // Commit imports all the pending transactions as a single block and starts a
 // fresh new state.
 func (b *SimulatedBackend) Commit() {

accounts/abi/bind/backends/simulated_test.go

@@ -38,6 +38,7 @@ func TestSimulatedBackend(t *testing.T) {
 	genAlloc[auth.From] = core.GenesisAccount{Balance: big.NewInt(9223372036854775807)}
 
 	sim := backends.NewSimulatedBackend(genAlloc, gasLimit)
+	defer sim.Close()
 
 	// should return an error if the tx is not found
 	txHash := common.HexToHash("2")