Question

I write extensions for a 3rd party application. The application calls my class libraries. I am unsuccessful in getting my assemblies to read from their app.config data when called from another program. Below reproduces the problem with a unit test.

App.config in ConsoleApplication.exe

<appSettings>
    <add key="testKey" value="testvalue" />
</appSettings>

    static void Main(string[] args)
    {
        TestClass c = new TestClass();
        c.Run();
    }

    //TestClass.Run()
    public void Run()
    {
        var readAppConfig = ConfigurationManager.AppSettings[0];
        MessageBox.Show("App config: " + readAppConfig);
    }

Unit test code, MSTEST

    [TestMethod]
    public void TestAppConfig()
    {
        TestClass c = new TestClass();
        c.Run();//fails here
    }

Main() works, TestAppConfig() fails with ArgumentOutOfRangeException

Index was out of range. Must be non-negative and less than the size of
the collection.

Do App.config stop working when called from external assemblies?

Answer 1

the app settings must be in the highest level component (in this case, your MSTEST app.config needs to hold the settings.