net.sourceforge.groboutils.junit.v1.iftc

Interface Testing

The Sun Java Tutorial indicates that classes which implement an interface "[sign] a contract" [1]. In some cases the contract has meta-data beyond the API declared in the interface source-code, such as "must never return null", usually declared in the JavaDoc. Forcing each implemented class to test this on its own is both poor coding practice and unenforcable. Instead, what we need is a way to write test cases for the interface, and each implemented class can execute an instance of that class against the tests. This framework eases this practice by extending the JUnit framework.

The interface creator creates a TestCase which extends InterfaceTest, commonly through InterfaceTestCase. The class to test need not be only an interface: in can be any kind of class.

Implemented classes need to use something like the following to test through an interface test:

import net.sourceforge.groboutils.junit.v1.iftc.*;
import junit.framework.*;

public MyClassTest extends TestCase {
    public MyClassTest( String name ) {
        super( name );
    }

    public static Test suite() {
        TestSuite suite = new TestSuite( MyClassTest.class )
        InterfaceTestSuite its = MyInterfaceTest.suite();
        its.addFactory( new CxFactory( "A" ) {
            public Object createImplObject() {
                return new MyClass( "string" );
            }
        } );
        its.addFactory( new CxFactory( "B" ) {
            public Object createImplObject() {
                return new MyClass( null );
            }
        } );
        suite.addTest( its );
        
        return suite;
    }
    ...
}

import net.sourceforge.groboutils.junit.v1.iftc.*;
import junit.framework.*;

public MyInterfaceTest extends InterfaceTestCase {
    public MyInterfaceTest( String name, ImplFactory f ) {
        super( name, MyInterface.class, f );
    }

    public static InterfaceTestSuite suite() {
        InterfaceTestSuite suite = new InterfaceTestSuite(
            MyInterfaceTest.class );
        
        return suite;
    }
    
    ...
}

References

1. Various. The Java Tutorial. Online at http://java.sun.com/docs/books/tutorial/java/interpack/usinginterface.html .

As of 08-Dec-2002, the original constructor will NOT add the owning class's name to the factory toString() output.