PosInfoMoq1003.md

PosInfoMoq1003: The Callback() method should be used to check the parameters when mocking a method with It.IsAny<T>() arguments

Property	Value
Rule ID	PosInfoMoq1003
Title	The Callback() method should be used to check the parameters when mocking a method with It.IsAny<T>() arguments
Category	Design
Default severity	Warning

Cause

A method has been setup with It.IsAny<T>() arguments without checking the parameters in a Callback() method.

Rule description

When setup a method using It.IsAny<T>() arguments, the parameters should be check in the Callback() method.

For example if we have the following code to test:

[Fact]
public class CustomerService
{
	private readonly ISmtpService smtpService;

	public CustomerService(ISmtpService smtpService)
	{
		this.smtpService = smtpService;
	}

	public void SendMail(string emailAddress)
	{
		this.smtpService.SendMail("[email protected]", emailAddress);
	}
}

If we mock the ISmtpService.SendMail() with a It.IsAny<string>() for the emailAddress argument, we can not check if the CustomerService.SendMail() has propagate correctly the value of the argument to the parameter of the ISmtpService.SendMail() method.

[Fact]
public void SendMail_ShouldCallSmtpService()
{
	var smtpService = new Mock<ISmtpService>();
	smtpService.Setup(s => s.SendMail("[email protected]", It.IsAny<string>()));	// With It.IsAny<string>() we can not check that emailAddress has been correctly passed in the CustomerService.SendMail() method.

	var service = new CustomerService(smtpService.Object);

	service.SendMail("Gilles");
}

The emailAddress parameter passed to the ISmtpService.SendMail() method should be tested with the Callback() method, when mocking the ISmtpService.SendMail() method with a It.IsAny<T>() argument.

[Fact]
public void SendMail_ShouldCallSmtpService()
{
	var smtpService = new Mock<ISmtpService>();
	smtpService.Setup(s => s.SendMail("[email protected]", It.IsAny<string>()))		// With It.IsAny() we should test the arguments if correctly propagated in the Callback() method.
		.Callback((string _, string emailAddress) =>
		{
			Assert.AreEqual("Gilles", em);	// Check the emailAddress parameter.
		});

	var service = new CustomerService(smtpService.Object);

	service.SendMail("Gilles");
}

Remarks

• If the parameters of mocked methods are very simple (primitive values for example), pass directly the expected value in the arguments of the method. For example

  smtpService.Setup(s => s.SendMail("[email protected]", "Gilles"))

  Instead of

  smtpService.Setup(s => s.SendMail("[email protected]", It.IsAny<string>()))

• Use the Callback() to assert complex parameters.

How to fix violations

To fix a violation of this rule, use the Callback() method to check the It.IsAny<T>() arguments.

When to suppress warnings

Do not suppress a warning from this rule. Normally It.IsAny<T>() arguments should be check and asserted in the Callback() methods.