add readme content about testnet, fix code syntax

README.md

@@ -173,6 +173,15 @@ bbgo pnl --exchange binance --asset BTC --since "2019-01-01"
 
 ## Advanced Configuration
 
+### Testnet (Paper Trading)
+
+Currently only supports binance testnet.
+To run bbgo in testnet, apply new API keys from [Binance Test Network](https://testnet.binance.vision), and set the following env before you start bbgo:
+```bash
+export PAPER_TRADE=1
+export DISABLE_MARKET_CACHE=1 # the symbols supported in testnet is far less than the mainnet
+```
+
 ### Notification
 
 - [Setting up Telegram notification](./doc/configuration/telegram.md)

pkg/exchange/binance/exchange.go

@@ -24,6 +24,7 @@ import (
 
 	"github.com/c9s/bbgo/pkg/fixedpoint"
 	"github.com/c9s/bbgo/pkg/types"
+	"github.com/c9s/bbgo/pkg/util"
 )
 
 const BNB = "BNB"
@@ -61,8 +62,8 @@ func isBinanceUs() bool {
 }
 
 func paperTrade() bool {
-	v, err := strconv.ParseBool(os.Getenv("PAPER_TRADE"))
-	return err == nil && v
+	v, ok := util.GetEnvVarBool("PAPER_TRADE")
+	return ok && v
 }
 
 type Exchange struct {

pkg/service/sync.go

@@ -3,8 +3,6 @@ package service
 import (
 	"context"
 	"errors"
-	"os"
-	"strconv"
 	"time"
 
 	"github.com/c9s/bbgo/pkg/cache"
@@ -12,6 +10,7 @@ import (
 	log "github.com/sirupsen/logrus"
 
 	"github.com/c9s/bbgo/pkg/types"
+	"github.com/c9s/bbgo/pkg/util"
 )
 
 var ErrNotImplemented = errors.New("not implemented")
@@ -26,8 +25,8 @@ type SyncService struct {
 }
 
 func paperTrade() bool {
-	v, err := strconv.ParseBool(os.Getenv("PAPER_TRADE"))
-	return err == nil && v
+	v, ok := util.GetEnvVarBool("PAPER_TRADE")
+	return ok && v
 }
 
 // SyncSessionSymbols syncs the trades from the given exchange session
@@ -51,7 +50,10 @@ func (s *SyncService) SyncSessionSymbols(ctx context.Context, exchange types.Exc
 		}
 	}
 
-	if !paperTrade() {
+	if paperTrade() {
+		return nil
+	}
+
 	log.Infof("syncing %s deposit records...", exchange.Name())
 	if err := s.DepositService.Sync(ctx, exchange); err != nil {
 		if err != ErrNotImplemented {
@@ -73,6 +75,6 @@ func (s *SyncService) SyncSessionSymbols(ctx context.Context, exchange types.Exc
 			return err
 		}
 	}
-	}
+
 	return nil
 }