How to unit test methods in windows form class?

Question

I have a developing a c# windows form application and I have a method that exists inside the main form class.

Imagine methodA as part of the main form class.

public void methodA() {
    A.someMethod();
    B.someMethod();

    // some more code

    if (someCondition) {
        // execute some code 
    }

    // initialize timer and set event handler for timer
    // run new thread 

    }

class A {
    someMethod() {...}
}

class B {
    someMethod() {...}
}

How would I run tests to test the branch logic of this methodA (isCondition)? since it involves initializing timer and running threads. Can i only verify the logic while doing system test ? I dont think it is possible to mock the timer and threading function.

Thank you !

Answer 1

Of course you can mock the timer. This is by creating a new interface, say, ITimerWrapper and implement it by using the concrete Timer class. Basically a wrapper of the Timer class. Then use that instead of the concrete Timer class you have.

Something in the tune of:

public partial class Form1 : Form
{
    private readonly ITimerWrapper _timerWrapper;
    public Form1(ITimerWrapper timerWrapper)
    {
        InitializeComponent();

        this._timerWrapper = timerWrapper; // of course this is done via dependency injection
        this._timerWrapper.Interval = 1000;
    }

    private void Form1_Load(object sender, EventArgs e)
    {
        // now you can mock this interface

        this._timerWrapper.AddTickHandler(this.Tick_Event);
        this._timerWrapper.Start();
    }

    private void Tick_Event(object sender, EventArgs e)
    {
        Console.WriteLine("tick tock");
    }
}

public interface ITimerWrapper
{
    void AddTickHandler(EventHandler eventHandler);
    void Start();
    void Stop();
    int Interval { get; set; }
}
public class TimerWrapper : ITimerWrapper
{
    private readonly Timer _timer;

    public TimerWrapper()
    {
        this._timer = new Timer();
    }

    public int Interval
    {
        get
        {
            return this._timer.Interval;
        }
        set
        {
            this._timer.Interval = value;
        }
    }

    public void AddTickHandler(EventHandler eventHandler)
    {
        this._timer.Tick += eventHandler;
    }

    public void Start()
    {
        this._timer.Start();
    }

    public void Stop()
    {
        this._timer.Stop();
    }
}

Then for the spinning of a new thread, that's also testable by doing the same thing.

Bottomline is to have an interface to separate concerns and mock the interface on your unit test.