Dynamic app.config settings for testing

If you need to write tests that verify behaviour based on different app.config settings, here’s a neat way of doing so.

In your [SetUp] method, load the app.config into two separate instances of the Configuration class, like so:

[SetUp]
public void SetUp()
{
//load config so it can be edited for tests
_originalConfig = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);

_currentConfig = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
//any other init code here
}


In your [TearDown] method, ensure that you restore the app.config to the original (presumably you want it to be the same every time your tests start).

[TearDown]
public void TearDown()
{
_currentConfig = _originalConfig;
_currentConfig.Save();
}


When you need to modify any part of the config you can do so (provided there’s a “set” property for the element or attribute) at runtime like so:


[Test]
public void MyTest()
{
//... set up stuff here ...

//modify config for this test. Set the lockout period to 120 minutes
//_client is an instance of a custom configuration element
int lockoutPeriod = 120;
_client.Profiles.PasswordLockoutPeriod = lockoutPeriod;
_currentConfig.Save();
ConfigurationManager.RefreshSection("clientSettings");

//... carry out your tests here ...
}


Pay particular attention to the call to ConfigurationManager.RefreshSection("clientSettings");. The change I made to the config is within this section and so I want to refresh it before continuing in order to ensure that the new version is used.

Also note that any objects that reference the config need to be re-loaded after you’ve modified (and refreshed) the config in order to get the changes. For example, if you have loaded an instance of a class in your SetUp that uses config you'll have to re-initialise that class after making your config changes in a test.