Unit Testing the App_Code of an ASP.Net Web Application

Question

I want to create an ASP.Net Web Application, and I want to write unit tests for it. But my unit test project can't see any of the types in my web application's App_Code directory.

Steps to reproduce

(skip down past the images if you already know how to create a default webforms web application and add an app_code folder)

Open Visual Studio. Choose File->New->Project.
Choose Templates -> Visual C# -> Web. Choose ASP.Net Web Application. Choose "OK".

Choose "Web Forms". Check "Add unit tests". Click OK.

In the solution explorer, right-click on the web application and choose "Add -> Add ASP.Net Folder -> App_Code".

Add a new item to App_Code, named "Util.cs". Add a function to the file so the contents are:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace WebApplication1.App_Code
{
    public class Util
    {
        public static int getMeaningOfLife()
        {
            return 42;
        }
    }
}

In the Unit Testing project, change UnitTest1.cs to:

using System;
using Microsoft.VisualStudio.TestTools.UnitTesting;

namespace WebApplication1.Tests
{
    [TestClass]
    public class UnitTest1
    {
        [TestMethod]
        public void TestMethod1()
        {
            int result = WebApplication1.App_Code.Util.getMeaningOfLife();
            if (result != 42)
            {
                Assert.Fail();
            }
        }
    }
}

Then build the project.

Expected behavior:

The solution should build. If we attempt to test, the test should succeed.

Actual behavior:

The solution fails to build with The type or namespace name 'App_Code' does not exist in the namespace 'WebApplication1' (are you missing an assembly reference?)

Other notes

I looked at Unit Testing ASP.net Web Site Project code stored in App_Code, but I don't think the problem exactly matches my circumstances because they're testing a website and I'm testing a web application. Some answers specifically suggest switching to a web application, implying that it would no longer be a problem:

However, if you have the option of segregating the code into binaries (class libraries) or just using a web application, I'd suggest that as a better alternative.

I would either move this logic out to its own class library project or change the project type to Web Application, as Fredrik and Colin suggest.

And as the OP stated it's also possible to move to a Web App project, which i would say is cleaner as well

The advice "try using a web application" doesn't apply to me, because I'm already using a web application, and it still doesn't work.

The answers also suggest "Try moving the code out to its own project", and I do expect that would work, but in my actual solution I have dozens of files in the App_Code directory. I would prefer not to perform any serious structural changes before I can establish a testing framework first.

Did you add a reference to the web project in the Unit Testing project? — JuanR
– JuanR, Commented Mar 2, 2017 at 16:44
You don't need an App_Code directory in a web application. That's for a website project. — mason
– mason, Commented Mar 2, 2017 at 16:49
App_Code is special folder, it will not get compiled in your assembly, but instead will be compiled at run-time by asp.net. So you cannot reference it from unit test, and actually you cannot use it even from your web application assembly (from global.asax for example). So - just don't put anything in that folder unless you know what you are doing and why. — Evk
– Evk, Commented Mar 2, 2017 at 16:51
@Juan, I tried, but web applications are not visible in the "Projects" panel of the Add Reference window, and AFAIK web applications don't compile to dlls, so I can't add a reference using the "browse" panel either. — Kevin
– Kevin, Commented Mar 2, 2017 at 16:55
If you want to use App_Code files as regular files, without their intended purpose (asp.net runtime compilation) - just right click your Util.cs file under App_Code, select Properties and change Build Action from "Content" to "Compile". Then you will be able to reference it everywhere, including unit test. There is nothing magical really in that folder name. — Evk
– Evk, Commented Mar 2, 2017 at 17:13

Evk · Accepted Answer · 2017-03-02 19:34:29Z

3

So to bring a bit more clarity. App_Code folder has special meaning in asp.net projects. You can put files there and asp.net will compile them at runtime and will monitor them for changes to recompile on the fly when something changes. Details are not very relevant, main thing is: if you don't need this feature - don't use App_Code folder.

However, there is nothing magical in that folder itself. When you create it via "Add ASP.NET folder" (or just manually in web site project) - Visual Studio will set build action of files you add there to Content, even for code files. Such files will not be compiled into resulting assembly, that is why you cannot use them from your Unit Test project, nor you can use it even from web site code itself. If you manually change build action to Compile - it will be compiled and can be used as usual. That's all the difference.

edited Mar 2, 2017 at 19:34

answered Mar 2, 2017 at 17:43

Evk

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5 Comments

Kevin Over a year ago

I believe this accurately answers the question as I have posed it. I see that if I move my util.cs file to anywhere else in the project, then I can properly unit test it. I'm still seeing some peculiar behavior in the non-mcve project I haven't shared here, but I suspect that's an unrelated issue, and would deserve its own post separate from this one. Case closed on this particular issue.

Evk Over a year ago

Note you can move it OR change build action to compile for it to work as you expect.

mason Over a year ago

Even if you're using Web Forms, you only need App_Code if you're doing a website (instead of web application). It's even possible to do an MVC website and put all your controllers etc in App_Code. So it's nothing special to do with Web Forms.

Evk Over a year ago

@mason that's right, I removed that. Though I have only even seens this to be used in old web forms projects, never in mvc ones.

mason Over a year ago

@Evk Well if you move it, and it's not set as compile, then you need to set it to compile. So really the solution is "set it to compile, and it'd be better not to put it in App_Code so you avoid confusion". And yeah, I was just learning MVC when I tried to put it in a website project instead of web application. It's not something I recommend trying.

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