起订量：从可空类型的模拟方法返回 null

Question

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?

Answer 1

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);
}