func Test_DrawNode_WhenVertexLabelReturnsError_ReturnsError(t *testing.T) {
    err := errors.New("test error")
    provider := new(MockPrintProvider)
    provider.On("VertexGetID", mock.Anything).Return(pp.VisibleString(""), nil)
    provider.On("VertexGetLabel", mock.Anything).Return(pp.VisibleString(""), err)