How to do unit testing for windows form application

Question

how to do unit testing for windows form application. I have create Form2 and i want test that form using nUnit , i got this error :

Message: System.TypeInitializationException : The type initializer for '...Form2' threw an exception. ----> System.Threading.ThreadStateException : ActiveX control '8856f961-340a-11d0-a96b-00c04fd705a2' cannot be instantiated because the current thread is not in a single-threaded apartment.

Test

[TestFixture,SingleThreaded]
public class FormTest
{

    [SetUp]
    public void Setup()
    {

    }
    [Test]
    public void Form_Test()
    {
        var form = new Form2();

    }
}

code : Form2

public partial class Form2 : Form
{
    public Form2()
    {
        InitializeComponent();
    }

    public void SomeThing()
    { 

    //something
    }
}

code : Form2.Designer

partial class Form2
{
    /// <summary>
    /// Required designer variable.
    /// </summary>
    private System.ComponentModel.IContainer components = null;

    /// <summary>
    /// Clean up any resources being used.
    /// </summary>
    /// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
    protected override void Dispose(bool disposing)
    {
        if (disposing && (components != null))
        {
            components.Dispose();
        }
        base.Dispose(disposing);
    }

    #region Windows Form Designer generated code

    /// <summary>
    /// Required method for Designer support - do not modify
    /// the contents of this method with the code editor.
    /// </summary>
    private void InitializeComponent()
    {
        this.webBrowser1 = new System.Windows.Forms.WebBrowser();
        this.SuspendLayout();
        // 
        // webBrowser1
        // 
        this.webBrowser1.Dock = System.Windows.Forms.DockStyle.Fill;
        this.webBrowser1.Location = new System.Drawing.Point(0, 0);
        this.webBrowser1.MinimumSize = new System.Drawing.Size(20, 20);
        this.webBrowser1.Name = "webBrowser1";
        this.webBrowser1.Size = new System.Drawing.Size(800, 450);
        this.webBrowser1.TabIndex = 0;
        // 
        // Form2
        // 
        this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
        this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
        this.ClientSize = new System.Drawing.Size(800, 450);
        this.Controls.Add(this.webBrowser1);
        this.Name = "Form2";
        this.Text = "Form2";
        this.ResumeLayout(false);

    }

    #endregion

    private System.Windows.Forms.WebBrowser webBrowser1;
}

Usually, Unit tests are written to test the existing code. You should reference the form in your windows forms application, not make a new one in your test. unless you are trying to mock something — Glenn van Acker, Dec 04 '19 at 07:48
Check [this](https://stackoverflow.com/questions/56567075/how-to-run-nunit-test-in-sta-thread) — Eldar, Dec 04 '19 at 07:52
@GlennvanAcker can you please provide some example of code . — sujan maharjan, Dec 04 '19 at 07:57
Can you show us the code you are testing first, then i can see where you're going with this. The answer below is actually correct. normally, you don't test your windows and your forms, but the businesslogic itself. — Glenn van Acker, Dec 04 '19 at 07:58
@GlennvanAcker, actually i don't want to test form event but to test business logic on it — sujan maharjan, Dec 04 '19 at 08:10
@sujanmaharjan that's the code for the form, which we're not testing. you need to add the business logic — Glenn van Acker, Dec 04 '19 at 09:09
@GlennvanAcker business logic inside form called **something** method — sujan maharjan, Dec 04 '19 at 09:21
I can't really make sense of that sentence, can you rephrase that? i don't see a something method. usually, you'd split the business logic from the form, so you could reuse it somewhere else. — Glenn van Acker, Dec 04 '19 at 09:23

score 1 · Answer 1 · answered Dec 04 '19 at 07:58

You don't. You don't unit test your Windows with all the logic backed into it. You extract a piece you'd like to test into some class or, even better, an interface and instantiate test targeting that particular instance. That's why it called a "unit" test: on the contrary to the "integration" or "end2end" test, it is responsible for testing standalone pieces of software apart from an outter world.

In addition to this, it is literally useless to test that new form indeed gets created. Better focus on your domain logic, which is always a main source of bugs and undesired effects.

score 0 · Answer 2 · answered Dec 04 '19 at 08:20

Exception error is pretty clear:

cannot be instantiated because the current thread is not in a single-threaded apartment.

Add SingleThreaded attribute to test fixture to tell Nunit to run test on single thread.
UI controls must to be execute on single thread.

[TestFixture, SingleThreaded]
public class FormTest
{
    public void Form_Test()
    {
        var form = new Form1();

    }
}

Don't try to categorize tests (unit, integrations, acceptance, feature, behaviour, e2e etc).
There are only two test categories Quick and Slow

Quick: are tests which executes fast, so developer can get feedback on written code as quick as possible.
Slow: are tests which executes slow, at this moment this is tests which touches some external resources (database, file system, web services or UI components).

Slow tests are slow to write and slow to run, but they provide important value in form of confidence that application works as expected.

Possibly in the future external resources can be accessed instantly, which provide possibility to write tests for whole application without mocking every single "unit".

For example these days database can be run "in-memory", which provide possibility to run tests without full mocking of data layer.

In your specific scenario, there are some libraries which allow you to test winforms application in convenient way, just search for it.

You can test Form class without UI as other normal classes, but as soon you try to touch UI component your tests will fail.

If you have some logic in the form, which can be executed without UI components being involved, move this logic in separate class and test this class on it's own.

How to do unit testing for windows form application

2 Answers2