Add regulator to GCS

Signed-off-by: Huu Nguyen <whoshuu@gmail.com>

registry/storage/driver/base/regulator_test.go

@@ -1,6 +1,7 @@
 package base
 
 import (
+	"fmt"
 	"sync"
 	"testing"
 	"time"
@@ -65,3 +66,33 @@ func TestRegulatorEnterExit(t *testing.T) {
 		}
 	}
 }
+
+func TestGetLimitFromParameter(t *testing.T) {
+	tests := []struct {
+		Input    interface{}
+		Expected uint64
+		Min      uint64
+		Default  uint64
+		Err      error
+	}{
+		{"foo", 0, 5, 5, fmt.Errorf("parameter must be an integer, 'foo' invalid")},
+		{"50", 50, 5, 5, nil},
+		{"5", 25, 25, 50, nil}, // lower than Min returns Min
+		{nil, 50, 25, 50, nil}, // nil returns default
+		{812, 812, 25, 50, nil},
+	}
+
+	for _, item := range tests {
+		t.Run(fmt.Sprint(item.Input), func(t *testing.T) {
+			actual, err := GetLimitFromParameter(item.Input, item.Min, item.Default)
+
+			if err != nil && item.Err != nil && err.Error() != item.Err.Error() {
+				t.Fatalf("GetLimitFromParameter error, expected %#v got %#v", item.Err, err)
+			}
+
+			if actual != item.Expected {
+				t.Fatalf("GetLimitFromParameter result error, expected %d got %d", item.Expected, actual)
+			}
+		})
+	}
+}