您如何测试已创建对象的新实例？

Question

I'm using C#, xUnit, and Moq for unit testing. I have an object with a property of a complex type. To "clear" the property and all its properties, I do this:

this.ComplexTypeInstance = new ComplexType();

Now I'm trying to assert that ComplexTypeInstance has been assigned to a brand new object. My first thought was to compare ComplexTypeInstance to new ComplexType() and see if they are equal. But to do something like that I think I'd have to override the equals operator. Is there any way to easily check that all properties are set to their defaults? Or is there a way to assert that I've newed up the object?

Answer 1

Or is there a way to assert that I've newed up the object?

Just compare the references between the old one and the new one using ReferenceEquals . If they are different, then the property has been replaced.

var origInstance = this.ComplexInstance;
... // Some operation
Assert.False(object.ReferenceEquals(this.ComplexInstance, origInstance));

Answer 2

After thinking about this a bit, there were a few different scenarios I came up with to make it easier to test:

1. Wrap the ComplexType in a factory sort of method. I didn't like this b/c it just means one more class to create, and I wanted to avoid having such a simple factory.

2. Extract and Override - Create a virtual method that allows me to remove the concrete dependency. Google "Extract and Override" if you have questions. I don't like this b/c if you don't know the technique it can seem weird.

3. Inject an anonymous function that returns a new instance of the object.

4. A co-worker mentioned I could have also used Mark Seeman's SemanticComparison to compare my property to a new object.

I ended up going with the third option, injecting it through the constructor, though my IOC container couldn't resolve it easily and I had to spend a couple minutes trying to get it to resolve a binding for it. But I got it working pretty well. Maybe I should have just created the factory. But I'm glad I took out the dependency from the class. At first I didn't want to b/c it seemed so simple.