Test infrastructure, part 1 - building the builders

The basic brick of a test infrastructure is the ability to easily instantiate and set properties on the domain object under test. This can be achieved with a builder object, as per below. This builder exposes a fluent interface (in the chaining of methods withId and withName) to improve readibility.


Given a domain object such as

public class DomainObject{

   public DomainObject (Integer id, String name){
     this.id = id;
     this.name = name;
   }

   public Object doSomething(){
      ...
   }
}

then the associate builder will be:

public class DomainObjectBuilder{
   private Integer id="123";
   private String name="defaultName";

   public DomainObject build(){
      return new CustomObject(id,name);
   }

   public DomainObjectBuilder withId(Integer anId){
      this.id = anId;
      return this;
   }

   public DomainObjectBuilder withName(String name){
      this.name = name;
      return name;
   }
}

and a test for a DomainObject will look like:

DomainObject anObject = new DomainObjectBuilder()
.withId("345").withName("someTest").build();
assertThat (anObject.doSomething, is(anExpectedResult));

An alternative approach would be to do without a builder and simply add setters on the domain object, setters which would be invoked during the tests. The major drawback of this technique is that adding setters breaks immutability.