Unit Testing: Selecting an Action from an MVC Controller

To fully test an MVC web site it is important to test (in isolation) the following:

1. The behaviour of controller actions
2. The behaviour of any custom action filters.
3. The decoration of action filter attributes on controller actions.

To test the 3rd point, you must use reflection to select the desired action from the controller.  The following method takes an action name and a Tuple array of “Type” and “String”. Used together this combination should be enough to isolate the desired action.  Note: an empty tuple array is used to define no input parameters, which a null tuple array specifies that this shouldn’t be used to restrict the action (in this case the action name must be null)

public MethodInfo SelectAction(Controller controller, string actionName, Tuple[] expectedParameters = null)
{
    var methods = controller.GetType().GetMethods(BindingFlags.Public | BindingFlags.Instance).Where(mi => mi.Name.Equals(actionName));
    if (expectedParameters != null)
    { 
        methods = methods.Where(mi => CompareParameters(mi.GetParameters(), expectedParameters));
    }
    if (methods.Count() == 1)
    {
        return methods.First();
    }
    var ex = new Exception((methods.Count() == 0) 
        ? "No matching actions could be found on controller" 
        : "More than one matching action could be found on controller"); 
    ex.Data.Add("Controller", controller.GetType()); 
    ex.Data.Add("Action", actionName); 
    if (expectedParameters != null)
    {
        var parameterList = new StringBuilder(); 
        foreach (var expectedParameter in expectedParameters)
        {
            if (parameterList.Length > 0) 
            {
                parameterList.Append(", "); 
            }
            parameterList.AppendFormat("{0} {1}", 
                expectedParameter.Item1.Name, expectedParameter.Item2);
        } 
        ex.Data.Add("ParameterList", string.Format("({0}", parameterList.ToString()));
    } 
    ex.Data.Add("Matching Actions", methods.Count()); 
    throw ex;
}

This can then be called using the simple format below.  This code confirms that the controller has two search actions.  One taking no input parameters, whilst the other takes a bound input model.

public MethodInfo SelectAction(Controller controller, string actionName, Tuple[] expectedParameters = null)
{
    MethodInfo action = null;
    Assert.DoesNotThrow(() => action = 
        SelectAction(new CustomerController((new MockHttpContext()).Object), 
            "Search", new Tuple[] { }));
    Assert.That(action.Name, Is.EqualTo("Search"));
  
    Assert.DoesNotThrow(() => action = 
        SelectAction(new CustomerController((new MockHttpContext()).Object), 
            "Search", new[] { new Tuple(typeof(CustomerSearchInputModel), "inputModel") }));
    Assert.That(action.Name, Is.EqualTo("Search"));
}

In the next post, I will cover how to use this to assert the decoration of action filter attributes.