Testing hard to test code with EasyMock

If you are into unit testing, you may find EasyMock quite useful. It is very valuable for making hard-to-test-code testable.

For example I recently was adding tab-switching via keyboard to Riena. The state of each tab is kept in an interface named INavigationNode which has about 40 methods (!). Creating a mock by hand for such a big interface would not be fun at all. With EasyMock it just takes is a call to:

ISubApplicationNode nodeA = EasyMock.createMock(ISubApplicationNode.class);

The code for determining the next tab, depends strictly on the isSelected property. Manipulating the return value of this method takes just another EasyMock call:

EasyMock.expect(nodeA.isSelected()).andReturn(true);

This tells EasyMock that nodeA.isSelected() will be called once and should return true.

After everything is set-up I switch from ‘record’ to ‘play-back’ mode:

EasyMock.replay(nodeA);

Here’s a full example of a test case:

  protected void setUp() throws Exception {
    super.setUp();
    handler = new SwitchSubApplication();
    nodeA = EasyMock.createMock(ISubApplicationNode.class);
    nodeB = EasyMock.createMock(ISubApplicationNode.class);
    nodeC = EasyMock.createMock(ISubApplicationNode.class);
  }

  public void testFindNextSubApplicationAtoB() {
    EasyMock.expect(nodeA.isSelected()).andReturn(true);
    EasyMock.replay(nodeA);

    ISubApplicationNode[] nodes = { nodeA, nodeB, nodeC };
    assertSame(nodeB, handler.findNextNode(nodes));
  }

This post barely scratches the surface. Curious? Read this nice EasyMock introduction.

Image: (c) *Micky/flickr. Licensed under creative commons.