MStest throwing errors for Class library using multiple config files

Question

I have created a class library MultipleConfigFiles, which has a method getConfigData. This method reads data from config files.

 public class Class1
    {
      public string getConfigData()
      {
        string configData = ConfigurationManager.AppSettings["key"].ToString();
        return configData;
      }
    }

Now I have a console application ConsoleAppConfig, in which I have given the reference of the class library.In the main method, I have created a object for the library class and called the method.

static void Main(string[] args)
        {
            Class1 c = new Class1();
            string data = c.getConfigData();
            Console.Write(data);    
        }

This console application has 2 different config files dev.config and prod.config. In the main App.config file , I have used configSource to map the appropriate config file.

<appSettings configSource="dev.config" />

Dev.config file looks like this:

<?xml version="1.0" encoding="utf-8" ?>
<appSettings>
    <add key="key" value="dev" />
</appSettings>

Till here it is working fine.That is, when I run the console app, the method returns dev.

Now,I have created a MSTest project for this class library.

public class Class1Tests
    {
        [TestMethod()]
        public void getConfigDataTest()
        {
            Class1 obj = new Class1();
            var result = obj.getConfigData();                
        }
    }

Now the problem is, when I run this test, it throws an error saying
"An exception of type 'System.NullReferenceException' occurred in MultipleConfigFiles.dll but was not handled in user code. Additional information: Object reference not set to an instance of an object."

Since the config files are in ConsoleApplication , the method is not able to read the appsetting variables from there. Is there any way I can maintain the configuration files globally so that both of them use individually , or is there any better way to handle this.

Any inputs are appreciated.Thanks.

You need to have app.config file in the UnitTest Project. When you run UnitTests it will not use the app.config of Console Application project. — Chetan, Jun 19 '18 at 06:02
Should I add just the app.config file or even dev.config and prod.config. In anycase, those files will be duplicated.If somebody changes in a config file in consoleapplication and forgot to do that in TestProject, there will be a ambiguity, which I want to avoid. So is there any other way where these files are maintained globally? — CrazyCoder, Jun 19 '18 at 06:07
If you want to run unit tests with some specific values of `AppSettgings` then you just need app.config and have values put in `` of app.config itself. If you want to run unit tests with data of dev and prod config files then you need to add all three files in the test project. — Chetan, Jun 19 '18 at 06:09
@CrazyCoder as an addition: you do not need to duplicate the files. Have a look at using ['Add as link' in Visual Studio](https://blogs.msdn.microsoft.com/zainnab/2010/11/12/linked-items-in-projects/). — rickvdbosch, Jun 19 '18 at 06:20
If you make a shortcut file it won't work, most people make copies (https://stackoverflow.com/a/11535980/495455), the better more time consuming way is to mock the ConfigurationManager. — Jeremy Thompson, Jun 19 '18 at 06:46
@JeremyThompson Can you show me how to mock the configurationmanager. Any example or sample code would be helpful — CrazyCoder, Jun 19 '18 at 06:59
@rickvdbosch I tried adding those files as links. It was giving an error "Unable to open configSource file 'dev.config'." — CrazyCoder, Jun 19 '18 at 07:00
You're going to have to add all of the files, and set them to be copied on build under Properties -> Copy to Output Directory. — rickvdbosch, Jun 19 '18 at 07:03
@rickvdbosch . In properties , there is no Copied on build. So I set them to Copy always. It worked. Thanks a lot. — CrazyCoder, Jun 19 '18 at 07:08
Hey, I will reopen if you need,, I didn't know YOU CAN ADD CONFIG TO OTHER PROJECTS AS LINKS! — Jeremy Thompson, Jun 19 '18 at 08:23
Weird even a trusted c# user I cannot close this as a duplicate: https://stackoverflow.com/a/1528427/495455 — Jeremy Thompson, Jun 19 '18 at 08:24
Closed in web browser as a duplicate, didn't work in SO app. Tell me if you want me to reopen. I don't want to hammer close this :) — Jeremy Thompson, Jun 19 '18 at 08:26

score 0 · Accepted Answer · answered Jun 19 '18 at 07:58

Without duplicating the files you can the Link the files in existing Unit Test project. You can try the same as mentioned in the image Link (https://grantwinney.com/content/images/2014/04/AddExistingFileAsLink-002.png)

Google this term "Visual Studio - Add File As Link" for more Info

Image Credits : https://grantwinney.com

MStest throwing errors for Class library using multiple config files

1 Answers1