accounting: factor --tpslimit code into accounting from fshttp

fs/accounting/tpslimit_test.go

@@ -0,0 +1,39 @@
+package accounting
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"github.com/rclone/rclone/fs"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestLimitTPS(t *testing.T) {
+	timeTransactions := func(n int, minTime, maxTime time.Duration) {
+		start := time.Now()
+		for i := 0; i < n; i++ {
+			LimitTPS(context.Background())
+		}
+		dt := time.Since(start)
+		assert.True(t, dt >= minTime && dt <= maxTime, "Expecting time between %v and %v, got %v", minTime, maxTime, dt)
+	}
+
+	t.Run("Off", func(t *testing.T) {
+		assert.Nil(t, tpsBucket)
+		timeTransactions(100, 0*time.Millisecond, 100*time.Millisecond)
+	})
+
+	t.Run("On", func(t *testing.T) {
+		ctx, ci := fs.AddConfig(context.Background())
+		ci.TPSLimit = 100.0
+		ci.TPSLimitBurst = 0
+		StartLimitTPS(ctx)
+		assert.NotNil(t, tpsBucket)
+		defer func() {
+			tpsBucket = nil
+		}()
+
+		timeTransactions(100, 900*time.Millisecond, 2000*time.Millisecond)
+	})
+}