Moq : Return null from a mocked method with nullable type-CodePudding

I have an implicit operator in an abstract class that is similar to below which converts the data to provided type.

public abstract class MyClass
{
    private object dataHolder; // just for representation
    // at implementation it tries to convert dataHolder object
    // or returns null if failed
    public abstract T? Convert<T>();
    public static implicit operator byte[]?(MyClass obj) => obj.Convert<byte[]?>();
}

I am trying to create unit tests for this class

[TestMethod]
public void MyTestMethod()
{
    Mock<MyClass> mockedClass = new() { CallBase = true };
    mockedClass.Setup(x => x.Convert<byte[]?>()); // no return statement
    // this should be null using implicit operator
    byte[]? output = mockedClass.Object;

    // however I am receiving an empty byte[] (length 0).
    Assert.IsNull(output);
}

How do I verify that my output can also be null?

CodePudding user response：

If you want to test that the implicit operator works as expected you could just verify that the expected underlying method was called.

Something like this;

[Test]
public void VerifyThatImplicitOperatorWorksAsExpected()
{
    Mock<MyClass> mockedClass = new() { CallBase = true };
    mockedClass.Setup(x => x.Convert<byte[]?>()).Returns<byte[]?>(null);
    byte[]? output = mockedClass.Object;

    Assert.IsNull(output);
    // Verify that the Convert method was called.
    mockedClass.Verify(x => x.Convert<byte[]?>(), Times.Once);
}