Hi,

 I am using JustMock for some app.config settings:

 Mock.Arrange(() => ConfigurationManager.AppSettings["MyAppSettingKey1"]).Returns("MyAppSettingValue1");​

Mock.Arrange(() => ConfigurationManager.AppSettings["MyAppSettingKey2"]).Returns("MyAppSettingValue2");​

Mock.Arrange(() => ConfigurationManager.AppSettings["MyAppSettingKey3"]).Returns("MyAppSettingValue3");​​

However, if I do this, other values that are not explicitly mocked are not available:

var myValue = ConfigurationManager.AppSettings["MyAppSettingKeyNotMocked"])

throws a System.NullReferenceException

Is there a better way to mock Configuration.AppSettings?

Hi Stefan,

thank you for your reply.  This does indeed work and solves my problem perfectly.  I don't fully understand your solution though.
I fail to see the difference between:

Mock.Arrange(() => ConfigurationManager.AppSettings["MyAppSettingKey1"]).Returns("MyAppSettingValue1");​

and 

var appSettings = ConfigurationManager.AppSettings;
Mock.Arrange(() => appSettings["MyAppSettingKey1"]).Returns("MyAppSettingValue1");​

Why does this retain the original behaviour for unarranged keys when my initial version doesn't?  I realise you are mocking the instance, but not of my subsequent code refers to this new variable directly.

Hi Stefan,

 thank you very much for a really clear explanation.  I now completely understand.

 Thanks again.