Home > Articles > Programming

📄 Contents

  1. Testing First
  2. How NUnit Works
  3. Writing Your First NUnit Test
  • Print
  • + Share This
Like this article? We recommend

Writing Your First NUnit Test

I always find thinking of a sample to be the hardest part of writing these tutorials. My NUnit sample is the product of an uninspired mind and an overweight body. Here then is my user story:

The component should provide conversions between pounds and kilos. Conversions should be accurate to two decimal places.

Writing the Sample

Now that you know what to write, go ahead and launch Visual Studio.NET and create a new VB.NET project of type "Class Library", naming it "Person". This will give you a shell class file (class1.vb). Edit class1.vb and add just enough code to define it:

Public Enum ConversionDirection
End Enum
Public Class Weight
Dim _kilos As Single
   Dim _pounds As Single
  Property Kilos() As Single
      Return _kilos
    End Get
    Set(ByVal Value As Single)
      _kilos = Value
    End Set
  End Property
  Property Pounds() As Single
      Return (_pounds)
    End Get
    Set(ByVal Value As Single)
      _pounds = Value
    End Set
  End Property
Sub Convert(ByVal direction As ConversionDirection)
End Sub
End Class

My class has two properties for kilos and pounds. The only method is for conversion. Don't get too hung-up on the "property versus passing parameters to convert" question—we're demonstrating NUnit here. You may have chosen to write even less code, leaving out the setter and getter code in the properties, for example. In my case, I figure that it was so simple that any problems would be caught at compile-time, anyway.

The class has enough definition now, so we'll put it to one side and write a unit test for it.

Writing the Unit Test

To create a NUnit test, you'll need to add a new Class Library project to your existing solution. Go ahead and do this now and name it PersonTest. The last step in preparing your project is to add a reference to the NUnit test framework DLL (nunit.framework.dll); you will find this in the bin folder of your installed directory. I installed NUnit in the default location of c:\Program Files\NUnit V2.0. Open up class1.vb in your test project and add this code (without the line numbers):

1 Imports System
2 Imports NUnit.Framework
3 <TestFixture()> Public Class PersonTests
5   Private oTest As Person.Weight
6   Public Sub New()
7     MyBase.New()
8   End Sub
9   <SetUp()> Public Sub Init()
10     oTest = New Person.Weight()
11   End Sub
12   <Test()>Public Sub TestKiloConversion()
13     System.Console.WriteLine("Running TestKiloConversion()")
14    With oTest
15       .Pounds = 100
16       .Convert(Person.ConversionDirection.PoundsToKilos)
17     End With
18     Assertion.AssertEquals("Failed to convert to Kilos!", "45.45", Format(oTest.Kilos, "#.00"))
19   End Sub
20 End Class

Rebuild your solution, and you're ready to run the test. Before you do that, I want to take a chance to explain how the unit test works. Hitting the tops of the waves we get the following:

  • Lines 1 and 2: I import or make a reference to the base System library and NUnit itself.

  • Line 3: The public method name for the test class: PersonTests denoted by the TestFixture attribute.

  • Line 5: I create a private variable to hold the instance of our Person class.

  • Line 6–8: Standard method constructor for the PersonTests class.

  • Line 9–11: I override the base setup method with my own and create an instance of the Person.Weight object.

  • Line 12–19: I test for the pounds-to-kilograms conversion. Line 20 sees me set the pounds to 100 and then I call the convert method. In line 21, I test the Kilos property and compare to the two-digit string result ("45.45"); the message will be displayed in the NUnit runner if the values are different. And, no, I don't weigh 100 pounds. The test is denoted by the Test() attribute – you can use any name for your test.

I'd like to make it a little more magical, but you'd see through me in no time. That's all there is to writing a unit test with NUnit: Create your object, make it do something, compare the result to what you expected, and make a rude noise if it's wrong. (Well, if not a rude noise, at the very least a curt message to the tester.) The Assert method comes in a number of overloaded flavors: Some take Booleans; others take strings and numeric. The one I'm using takes three parameters:

  • Message string—The message to be displayed if the test fails.

  • Expected result string—the correct result.

  • Actual result string—the result returned by my object.

Ok, now you can run your test. You can do this in three ways:

  • Use the command-line test runner.

  • Use the GUI test runner.

  • Run the project from inside Visual Studio.NET and launch the GUI from there.

Clearly, the last option is the coolest, but you have to run before you can walk. Besides, I want to leave that for my next article-maximum dramatic effect. So, let's run the test from the GUI.

Select your PersonTest binary (PersonTest.dll under the bin folder). Run the test, and you should get the display shown in Figure 3.

Figure 3Figure 3 The example test failing inside NUnit.

Yet another red bar—this is becoming a habit. Considering there is no working code in Person class yet, I'd be concerned if the test passed. One point to note: You can keep the runner window open as you work and simply press "Run" without doing a reload.

Finishing the Test

Go back to the Person class and add the code you need to pass the test. Remember: Your goal is pass the test, not to make perfect code. The listing below is my version of Person the class (hey, don't knock it; at least it works).

1 Public Enum ConversionDirection
2   KiloToPounds
3   PoundsToKilos
4 End Enum
5 Public Class Weight
6   Const CONVERSION_FACTOR As Single = 2.2
7   Dim _kilos As Single
8   Dim _pounds As Single
9   Property Kilos() As Single
10     Get
11       Return _kilos
12     End Get
13     Set(ByVal Value As Single)
14       _kilos = Value
15     End Set
16   End Property
17   Property Pounds() As Single
18     Get
19       Return (_pounds)
20     End Get
21     Set(ByVal Value As Single)
22       _pounds = Value
23     End Set
24   End Property
25  Sub Convert(ByVal direction As ConversionDirection)
26     If direction = ConversionDirection.KiloToPounds Then
27       _pounds = _kilos * CONVERSION_FACTOR
28     Else
29       _kilos = _pounds / CONVERSION_FACTOR
30     End If
31   End Sub
32 End Class

I went back to my Convert method and added some highly complex code to convert to either U.S. or metric weight measurements. I'd like some kind of credit if you use this code in your next killer app. (Naming a child after me would suffice.) Press Run again on the Test Runner and you should see the happy picture shown in Figure 4.

Figure 4Figure 4 The example test passing inside NUnit.

Green At Last, I'm Green At Last

Green at last! Now you have a rock-solid test for the kilo conversion. This means you can dive back into the Person class and refactor to your heart's content.

Refactoring means changing the way your code is written without changing the object's external interfaces. Martin Fowler is the unofficial "keeper of the flame" when it comes to refactoring. Buy his book or visit his site (http://www.refactoring.com).


"Refactoring – Improving the design of existing code" by Martin Fowler, Addison Wesley, 1999

Over the last few minutes, you've seen how NUnit supplies you with a simple yet powerful tool for unit testing. NUnit isn't for XP-ers alone! Start using it to test today by doing these steps:

  1. Create your stub class.

  2. Create a test in your NUnit test harness for the class.

  3. Run the test.

  4. Add code to your class and retest until it passes.

Next time around, I'll show you some more tricks with NUnit, including how to run it from Visual Studio.NET.

Now where are those scales...?

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020