Java – Unit testing when you have no getters and setters

I cannot put the object into the state needed to perform the tests.

If you cannot put the object into the state needed to perform a test, then you cannot put the object into the state in production code, so there's no need to test that state. Obviously, this isn't true in your case, you can put your object into the needed state, just call Approve.

• I cannot publish unless the Document has been approved: write a test that calling publish before calling approve causes the right error without changing the object state.

  void testPublishBeforeApprove() {
      doc = new Document("Doc");
      AssertRaises(doc.publish, ..., NotApprovedException);
  }
  

• I cannot re-publish a Document: write a test that approves an object, then calling publish once succeed, but second time causes the right error without changing the object state.

  void testRePublish() {
      doc = new Document("Doc");
      doc.approve();
      doc.publish();
      AssertRaises(doc.publish, ..., RepublishException);
  }
  

• When published, the PublishedBy and PublishedOn values are properly set: write a test that calls approve then call publish, assert that the object state changes correctly

  void testPublish() {
      doc = new Document("Doc");
      doc.approve();
      doc.publish();
      Assert(doc.PublishedBy, ...);
      ...
  }
  

• When publised, the PublishedEvent is raised: hook to the event system and set a flag to make sure it's called

You also need to write test for approve.

In other word, don't test the relation between internal fields and IsPublished and IsApproved, your test would be quite fragile if you do that since changing your field would mean changing your tests code, so the test would be quite pointless. Instead you should test the relationship between calls of public methods, this way, even if you modify the fields you wouldn't need to modify the test.

Kinds of objects

For purposes of our discussion, let's separate our objects into three different kinds:

Business Domain logic

These are the objects that get work done. They move money from one checking account to another, fulfill orders, and all of the other actions that we expect business software to take.

Domain logic objects normally do not require accessors (getters and setters). Rather, you create the object by handing it dependencies through a constructor, and then manipulate the object through methods (tell, don't ask).

Data Transfer Objects

Data Transfer Objects are pure state; they don't contain any business logic. They will always have accessors. They may or may not have setters, depending on whether or not you're writing them in an immutable fashion. You will either set your fields in the constructor and their values will not change for the lifetime of the object, or your accessors will be read/write. In practice, these objects are typically mutable, so that a user can edit them.

View Model objects

View Model objects contain a displayable/editable data representation. They may contain business logic, usually confined to data validation. An example of a View Model object might be an InvoiceViewModel, containing a Customer object, an Invoice Header object, and Invoice Line Items. View Model objects always contain accessors.

So the only kind of object that will be "pure" in the sense that it doesn't contain field accessors will be the Domain Logic object. Serializing such an object saves its current "computational state," so that it can be retrieved later to complete processing. View Models and DTO's can be freely serialized, but in practice their data is normally saved to a database.

Serialization, dependencies and coupling

While it is true that serialization creates dependencies, in the sense that you have to deserialize to a compatible object, it does not necessarily follow that you have to change your serialization configuration. Good serialization mechanisms are general purpose; they don't care if you change the name of a property or member, so long as it can still map values to members. In practice, this only means that you must re-serialize the object instance to make the serialization representation (xml, json, whatever) compatible with your new object; no configuration changes to the serializer should be necessary.

It is true that objects should not be concerned with how they are serialized. You've already described one way such concerns can be decoupled from the domain classes: reflection. But the serializer should be concerned about how it serializes and deserializes objects; that, after all, is its function. The way you keep your objects decoupled from your serialization process is to make serialization a general-purpose function, able to work across all object types.

One of the things people get confused about is that decoupling has to occur in both directions. It does not; it only has to work in one direction. In practice, you can never decouple completely; there is always some coupling. The goal of loose coupling is to make code maintenance easier, not to remove all dependencies.