message: Fix gradients test in golang
  1. fix some test name.
  2. add test for existing prefix.
diff: @@ -223,7 +223,7 @@ func TestGraphAddGradientsSums(t *testing.T) {
  }
  }
  -func TestGraphAddGradientsWithInitialValuesToGraph(t *testing.T) {
  +func TestGraphAddGradientsWithInitialValues(t *testing.T) {
  g := NewGraph()
  x, err := Placeholder(g, "x", Float)
  op0, err := g.AddOperation(OpSpec{
  @@ -332,4 +332,9 @@ func TestGraphValidateGradientsNames(t *testing.T) {
  if !strings.HasPrefix(grads3[0].Op.Name(), "even_more_gradients/") {
  t.Fatalf("Got name %v, wanted started with even_more_gradients/", grads3[0].Op.Name())
  }
  +
  + _, err = g.AddGradients("even_more_gradients", []Output{y0}, []Output{x}, nil)
  + if err == nil {
  + t.Error("AddGradients should have failed if gradients name is already existing")
  + }
  }
  