error when token is empty

Signed-off-by: Victor Vieux <vieux@docker.com>

discovery/token/token.go

@@ -2,6 +2,7 @@ package token
 
 import (
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io/ioutil"
 	"net/http"
@@ -31,6 +32,10 @@ func (s *TokenDiscoveryService) Initialize(urltoken string, heartbeat int) error
 		s.url = DISCOVERY_URL
 		s.token = urltoken
 	}
+
+	if s.token == "" {
+		return errors.New("token is empty")
+	}
 	s.heartbeat = heartbeat
 
 	return nil

discovery/token/token_test.go

@@ -8,13 +8,18 @@ import (
 
 func TestInitialize(t *testing.T) {
 	discovery := &TokenDiscoveryService{}
-	discovery.Initialize("token", 0)
+	err := discovery.Initialize("token", 0)
+	assert.NoError(t, err)
 	assert.Equal(t, discovery.token, "token")
 	assert.Equal(t, discovery.url, DISCOVERY_URL)
 
-	discovery.Initialize("custom/path/token", 0)
+	err = discovery.Initialize("custom/path/token", 0)
+	assert.NoError(t, err)
 	assert.Equal(t, discovery.token, "token")
 	assert.Equal(t, discovery.url, "https://custom/path")
+
+	err = discovery.Initialize("", 0)
+	assert.Error(t, err)
 }
 
 func TestRegister(t *testing.T) {