AdMob test device ID acquisition for Unity (Checked unity version: 5.2.3p2)

AdMobUtility.cs

using UnityEngine;
using Cryptography = System.Security.Cryptography;
using System.Text;

#if UNITY_IOS
using UnityEngine.iOS;
#endif

/// <summary>
/// AdMobUtility
/// </summary>
public static class AdMobUtility
{
	/// <summary>
	/// Gets the test device identifier.
	/// </summary>
	/// <returns>The test device identifier.</returns>
	public static string GetTestDeviceId()
	{
#if UNITY_IOS
		return Device.advertisingIdentifier.CalculateMD5Hash();
#elif UNITY_ANDROID			
		return GetAndroidId().CalculateMD5Hash().ToUpper();
#else
		return "";
#endif
	}

#if UNITY_ANDROID

	/// <summary>
	/// Gets the android identifier.
	/// </summary>
	/// <returns>The android identifier.</returns>
	public static string GetAndroidId()
	{
		AndroidJavaClass unityPlayer = new AndroidJavaClass ("com.unity3d.player.UnityPlayer");
		AndroidJavaObject currentActivity = unityPlayer.GetStatic<AndroidJavaObject> ("currentActivity");
		AndroidJavaObject contentResolver = currentActivity.Call<AndroidJavaObject> ("getContentResolver");  
		AndroidJavaClass secure = new AndroidJavaClass ("android.provider.Settings$Secure");
		string name = secure.GetStatic<string>("ANDROID_ID");
		string androidId = secure.CallStatic<string>("getString", contentResolver, name);
		return androidId;
	}

#endif
	

	#region MD5

	/// <summary>
	/// Gets the ASCII bytes.
	/// </summary>
	/// <returns>The ASCII bytes.</returns>
	/// <param name="str">String.</param>
	public static byte[] GetASCIIBytes(this string str)
	{
		byte[] result = new byte[str.Length];
		for (int i = 0; i < str.Length; ++i) {
			char ch = str[i];
			result[i] = (byte)((ch < (char)0x80) ? ch : '?');
		}

		return result;
	}

	/// <summary>
	/// Calculates the MD5 hash.
	/// </summary>
	/// <returns>The MD5 hash.</returns>
	/// <param name="input">Input.</param>
	public static string CalculateMD5Hash(this string input)
	{
		return input.GetASCIIBytes().CalculateMD5Hash();
	}

	/// <summary>
	/// Calculates the MD5 hash.
	/// </summary>
	/// <returns>The MD5 hash.</returns>
	/// <param name="input">Input.</param>
	public static string CalculateMD5Hash(this byte[] input)
	{
		var hash = Cryptography.MD5.Create().ComputeHash(input);
		var sb = new StringBuilder();
		foreach (var b in hash) {
			sb.Append(b.ToString("x2"));
		}
		return sb.ToString();
	}


	#endregion
}

Thank you! So helpful.

Thanks for your code! Very helpful
I believe for Android you can simply use:
SystemInfo.deviceUniqueIdentifier.ToUpper()