Null exception for public variable

Hello! I have been trying to get one script to read input from another. I have this script so far:

The sender script:

using UnityEngine;
using System.Collections;

public class Test: MonoBehaviour 

{
	public jumpAfterTest _jumpAfterTest;

	void OnMouseDown() 
	{
		Debug.Log ("Mouse Down");

		_jumpAfterTest.JAT ();
	}

void OnMouseUp()
	{
		Debug.Log ("Mouse up");

	}
	
}

And the receiver script:

using UnityEngine;
using System.Collections;

public class jumpAfterTest : MonoBehaviour 
{   
	public void JAT()
	{
		Debug.Log("Me is JAT");
	}
}

The error I am getting is:

NullReferenceException: Object reference not set to an instance of an object
Test.OnMouseDown () (at Assets/my-scripts/Test.cs:13)
UnityEngine.SendMouseEvents:DoSendMouseEvents(Int32, Int32)

I am guessing that this error has to do with line 13 of test script: _jumpAfterTest.JAT ();

How would I fix this? Thanks for the help! I am in mobile, by the way.

Did you set the script in the inspector?

Click the object that has the Test script component attatched.
Then drag and drop the gameobject that has the jumpAfterTest attatched to the public _jumpAfterTest slot.

Hello in the Test script add this code in the start function
_jumpAfterTest = GetComponent<_jumpAfterTest>(); This should work if the receiver script is in another GameObject.