SuccessfulOnly(t *testing.T) {  tt := test.Start(t).Scenario("failed_transactions")  defer tt.Finish()   q := &Q{tt.HorizonSession()}  query := q.Operations().   OnlyPayments().   ForAccount("GBXGQJWVLWOYHFLVTKWV0FGHA0LNYY0JQKM0OAJAUEQFU0LPCSEFVXON")   operations, transactions, err := query.Fetch()  tt.Assert.NoError(err)  tt.Assert.Len(transactions, 0)   tt.Assert.Equal(0, len(operations))   for _, operation := range operations {   tt.Assert.True(operation.TransactionSuccessful)  }   sql, _, err := query.sql.ToSql()  tt.Assert.NoError(err)  // Note: brackets around `(ht.successful = true OR ht.successful IS NULL)` are critical!  tt.Assert.Contains(sql, "WHERE hop.type IN (?,?,?,?,?) AND hopp.history_account_id = ? AND (ht.successful = true OR ht.successful IS NULL)") }  // Test