ConfigurationManager.AppSettings Returns Null In Unit Test Project

Question

I have a C# unit test project with application settings in the app.config file. I am testing a class that exists in a different project. That class depends on bot

Answer 1

Consider refactoring your code that accesses the config to use a wrapper. Then you can write mocks for the wrapper class and not have to deal with the importing of the configuration file for the test.

In a library that is common to both, have something like this:

public interface IConfigurationWrapper {

    string GetValue(string key);
    bool HasKey(string key);
}

Then, in your libraries that need to access config, inject an instance of this interface type into the class that needs to read config.

public class MyClassOne {
    
    private IConfigurationWrapper _configWrapper;

    public MyClassOne(IConfigurationWrapper wrapper) {
        _configWrapper = wrapper;
    } // end constructor

    public void MethodThatDependsOnConfiguration() {
        string configValue = "";
        if(_configWrapper.HasKey("MySetting")) {
            configValue = _configWrapper.GetValue("MySetting");
        }
    } // end method

} // end class MyClassOne

Then, in one of your libraries, create an implementation that depends on the config file.

public class AppConfigWrapper : IConfigurationWrapper {
    
    public string GetValue(string key) {
        return ConfigurationManager.AppSettings[key];
    }

    public bool HasKey(string key) {
       return ConfigurationManager.AppSettings.AllKeys.Select((string x) => x.ToUpperInvariant()).Contains(key.ToUpperInvariant());
    }
}

Then, in the code that calls your class.

//Some method container
MyClassOne dataClass = new MyClassOne(new AppConfigWrapper());

dataClass.MethodThatDependsOnConfiguration();

Then in your test, you are free from dependency bondage. :) You can either create a fake version that implements IConfigurationWrapper and pass it in for your test, where you hard-code the return values from the GetValue and HasKey functions, or if you're using a mocking library like Moq:

Mock fakeWrapper = new Mock();

fakeWrapper.Setup((x) => x.GetValue(It.IsAny)).Returns("We just bypassed config.");

MyClassOne testObject = new MyClassOne(fakeWrapper.Object);
testObject.MethodThatDependsOnConfiguration();

Here is an article that covers the concept (albeit, for web forms, but the concepts are the same): http://www.schwammysays.net/how-to-unit-test-code-that-uses-appsettings-from-web-config/