make sure the value of the dangling filter is correct

Signed-off-by: Shijiang Wei <mountkin@gmail.com>

integration-cli/docker_cli_images_test.go

@@ -7,6 +7,7 @@ import (
 	"strings"
 	"time"
 
+	"github.com/docker/docker/pkg/integration/checker"
 	"github.com/docker/docker/pkg/stringid"
 	"github.com/go-check/check"
 )
@@ -197,3 +198,9 @@ func (s *DockerSuite) TestImagesEnsureDanglingImageOnlyListedOnce(c *check.C) {
 		c.Fatalf("expected 1 dangling image, got %d: %s", a, out)
 	}
 }
+
+func (s *DockerSuite) TestImagesWithIncorrectFilter(c *check.C) {
+	out, _, err := dockerCmdWithError("images", "-f", "dangling=invalid")
+	c.Assert(err, check.NotNil)
+	c.Assert(out, checker.Contains, "Invalid filter")
+}