Properly set default local threshold in Client

GODRIVER-1226

Change-Id: I7fcc5b09a49b80908d04f3c4fde75b6958748b5f

Author: skriptble

mongo/client.go

@@ -348,6 +348,7 @@ func (c *Client) configure(opts *options.ClientOptions) error {
 		func(...string) []string { return hosts },
 	))
 	// LocalThreshold
+	c.localThreshold = defaultLocalThreshold
 	if opts.LocalThreshold != nil {
 		c.localThreshold = *opts.LocalThreshold
 	}

mongo/client_test.go

@@ -36,6 +36,15 @@ func ExampleClient_Connect() {
 
 func TestClient(t *testing.T) {
 	t.Run("Can configure LocalThreshold", func(t *testing.T) {
+		t.Run("Should have default LocalThreshold set", func(t *testing.T) {
+			client := new(Client)
+			err := client.configure(options.Client())
+			noerr(t, err)
+			want, got := defaultLocalThreshold, client.localThreshold
+			if got != want {
+				t.Errorf("Default LocalThreshold not set on client. got %v; want %v", got, want)
+			}
+		})
 		opts := options.Client().SetLocalThreshold(10 * time.Second)
 		client := new(Client)
 		err := client.configure(opts)

x/mongo/driver/operation.go

@@ -24,6 +24,8 @@ import (
 	"go.mongodb.org/mongo-driver/x/mongo/driver/wiremessage"
 )
 
+const defaultLocalThreshold = 15 * time.Millisecond
+
 var dollarCmd = [...]byte{'.', '$', 'c', 'm', 'd'}
 
 var (
@@ -192,7 +194,7 @@ func (op Operation) selectServer(ctx context.Context) (Server, error) {
 		}
 		selector = description.CompositeSelector([]description.ServerSelector{
 			description.ReadPrefSelector(rp),
-			description.LatencySelector(15 * time.Millisecond),
+			description.LatencySelector(defaultLocalThreshold),
 		})
 	}