PosInformatique.Moq.Analyzers

PosInfoMoq2000: The Returns() or ReturnsAsync() methods must be call for Strict mocks

Property	Value
Rule ID	PosInfoMoq2000
Title	The Returns() or ReturnsAsync() methods must be call for Strict mocks
Category	Compilation
Default severity	Error

Cause

A Returns() or ReturnsAsync() of an Mock<T> instance with Strict behavior has not been called after a Setup() call.

Rule description

When a Mock<T> has been defined with the Strict behavior, the Returns() or ReturnsAsync() methods must be call when setup a method to mock which returns a value.

[Fact]
public void GetCustomer_ShouldCallRepository()
{
	// Arrange
	repository = new Mock<IRepository>(MockBehavior.Strict);
	repository.Setup(r => r.GetData());		// No Returns() method has been specified.
	...
	...
	// A MoqException will be thrown when the GetData() method will be called.
}

How to fix violations

To fix a violation of this rule, call the Returns() or ReturnsAsync() method after the Setup() call to setup the method to mock.

For example with the following code:

public interface IRepository
{
    int GetData();
}

public class CustomerService
{
	private readonly IRepository repository;

    public CustomerService(IRepository repository)
	{
		this.repository = repository;
	}

	public int GetDataFromRepository()
	{
		return this.repository.GetData();
	}
}

For the associated unit test, the Returns() method have to be called for the GetData() method setup.

[Fact]
public void GetCustomer_ShouldCallRepository()
{
	// Arrange
	repository = new Mock<IRepository>(MockBehavior.Strict);
	repository.Setup(r => r.GetData())
		.Returns(1234);					// The Returns() method is mandatory.

	var service = new CustomerService(repository.Object);

	// Act
	var result = service.GetDataFromRepository();

	// Arrange
	result.Should().Be(1234);
}

When to suppress warnings

Do not suppress an error from this rule. If bypassed, the execution of the unit test will be failed with a MoqException thrown with the “Invocation needs to return a value and therefore must have a corresponding setup that provides it.” message.

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