Equivalence

The tester checks whether the two given objects are equivalent according to the user-defined function object that implements the Equivalence interface.

The Equivalence interface is defined as:

public interface Equivalence<T>{
  public boolean equivalent(T t1, T t2);
}

It is assumed, but not required, that the implementation of the Equivalence interface represents a true equivalence relation, i.e. is reflexive, symmetric and transitive.

The following example illustrates the use of the checkEquivalent tests:

For the class that represents a Book with an Author we define two books to be equivalent if their author has the same name:

public class EquivBooks implements Equivalence<Book>{

  // two books are equivalent if the author's names match
  public boolean equivalent(Book b1, Book b2){
    return b1.author.name.equals(b2.author.name);
 }
}

We now run the following tests:

// sample books
public Author author1=new Author("author1",40);
public Author author2=new Author("author2",55);
public Author author3=new Author("author1",66);
public Author author4=new Author("author4",26);
  
// sample authors
public Book book1=new Book("title1",author1,4000); 
public Book book2=new Book("title2",author2,4000);
public Book book3=new Book("title3",author3,3001);
public Book book4=new Book("title1",author4,4000);

// instance of the Equivalence
Equivalence equbooks = new EquivBooks();

void testEquivalence(Tester t){
  t.checkEquivalent(this.book1, this.book2, equbooks, 
    "fails: different books, authors");
  t.checkEquivalent(this.book1, this.book3, equbooks, 
    "should succeed - same author names");
  t.checkEquivalent(this.book1, this.book4, equbooks, 
    "fails: different authors.");
  t.checkEquivalent(this.book1, this.book3, equbooks); // no testname
}

Code sources

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