概要

using System.Reflection;
using UnityEditor;

internal static class Example
{
    [MenuItem( "Tools/Example" )]
    private static void Hoge()
    {
        var assembly = Assembly.Load( "UnityEditor.TestRunner" );
        var type     = assembly.GetType( "UnityEditor.TestTools.TestRunner.TestRunnerWindow" );

        EditorWindow.GetWindow( type );
    }
}