public void HtmlConverter_AddPluginsOnceTest()
{
var plugin1 = new object();
var plugin2 = new object();
var r = _instance.AddPlugins(plugin1, plugin2);
Assert.AreSame(_instance, r);
Assert.AreEqual(2, _instance.Plugins.Count);
Assert.AreSame(_instance.Plugins[0], plugin1);
Assert.AreSame(_instance.Plugins[1], plugin2);
AssertRebuildProcessing();
}