CSharp example of using Rhino Mock constraints

Jan 13, 2013 00:00 · 301 words · 2 minute read Programming RhinoMock Test

What is Rhino Mock constraint?

constraint help us to check that method arguments or properties values are matching with our criteria or not [ more info ].


Injecting dependencies into production code is not always easy and simple . Sometimes you come across with other scenarios such as below

public void SetupAndRegisterNewDevice(int id,string name) { 
	Device device=new Device(){Id = id,Name = name};
	_deviceManager.AddedSucessfully = true;
	_deviceManager.special = _deviceManager.IsSpecialProduct(device) ? "Special" : "Not Special";

If you want to assert that the Add method called with below code

public void Given_Name_Id_When_SetupAndRegisterNewDevice_then_AddSameDeviceType() {
	var deviceManager = MockRepository.GenerateMock<IDeviceManager>();
	var machine = new Machine(deviceManager);
	var device = new Device { Id = 1, Name = "printer" };


	deviceManager.AssertWasCalled(x => x.Add(device));

It will be failing as the device instances are not the same. In this case we can use constraint and validate the input values of the Add method with Matches constraint.

deviceManager.AssertWasCalled(x => x.Add(Arg<Device>.Matches(y=>y.Id==device.Id && y.Name==device.Name)));

If we don’t care about the input type and just want to check the code flow we can come up with something like this

deviceManager.AssertWasCalled(x => x.Add(Arg<Device>.Is.Anything));

Or just check that it is it null or not

deviceManager.AssertWasCalled(x => x.Add(Arg<Device>.Is.NotNull));

Text constraint

It is also possible to evaluate the values of properties that match with your desire pattern or not . For instance to check if the Special property has “Special” term in its value you can write

deviceManager.AssertWasCalled(x => x.special = Arg<string>.Matches(Rhino.Mocks.Constraints.Text.Like("Special")));

List constraints

Rhino constraints also help us to check the list values.

public void RegisterDevices(List<Device> devices) {

We can check that if the passing list matches with our criteria or not

deviceManager.AssertWasCalled(x => x.AddAll(Arg<List<Device>>.List.IsIn(device1)));
deviceManager.AssertWasCalled(x => x.AddAll(Arg<List<Device>>.List.Count(Rhino.Mocks.Constraints.Is.Equal(3))));
deviceManager.AssertWasCalled(x => x.AddAll(Arg<List<Device>>.List.ContainsAll(deviceList)));


Feel free to download the source code of this example from my [ GitHub ]