should.js | BDD style assertions for node.js -- test framework | Functional Testing library

Yes. From should documentation

should.equal(actual, expected, [message])

Node.js standard assert.equal.

And from Nodejs documentation we know that assert.equal(...)

Tests shallow, coercive equality between the actual and expected parameters using the Abstract Equality Comparison ( == ).

Looks like you need to use eql(..) or deepEqual(..). Something like

First, be aware that done() implies a synchronous test; Mocha's default is to run tests asynchronously. If you want to test the 'returned' value from asynchronous functions (functions that return a value in a callback function), you run them synchronously, via done().

Next, you can't return a value from an asynchronous function. These two behaviours are mutually exclusive:

If a definition has already assigned the Assertion interface to Object.should globally (which it must have if you are told you are making a subsequent declaration)...

And if you have extended the original Assertion interface....

Then you don't need to re-specify the interface in a global declaration.

When you write multiple interface definitions within the same common root, they all contribute to a single type. That means your additions to an interface are included as if they were within the same code block.

If you get the error you mention, or if you can't see the type information you believe you added to the interface it will be because you haven't managed to hit the same common root, i.e. an interface exists in X.Y.Z but you have added it to X.Y.