Easy way to fill up ResultSet with data

Question

I want to mock a ResultSet. Seriously. I'm refactoring one big complicated piece of code which is parsing data from ResultSet, and I want my code to behave identically. So, I need to write a unit test for the piece being refactored to be able to test this.

After googling I came up with 2 ideas:

1. Use EasyMock, write looooong mocking sequence. VERY BAD solution: hard to add initial data, hard to change data, big test debugging promices.
2. Use Apache Derby or HSQLDB to create in-memory DB, fill it from file or String array, query with some magical InMemoryDBUtils.query(sql). Then use that ResultSet. Unfortunately, I did not find any magical InMemoryDBUtils to write the test fast :-). IBM article "Isolated unit testing of persistence with Derby" seems just fine about what I need, though...

Second approach looks somewhat easier and much more supportable.

What would you advice for creating such a mock? (despite doctors, of course :-)? Am I missing an eyebrow some silver bullet? Possibly, DBUnit is the tool for this?

Answer 1

DBUnit doesn't present a result set, to my knowledge, although it will well help you populate your in memory database.

I would say that a mocking framework is the wrong approach at this point. Mocking is about testing behavior and interaction, not just returning data, so it will likely get in your way.

I would instead either implement a result set interface, or create a dynamic proxy of a result set interface to a class that implements the methods you care about without having to implement the whole result set. You will likely find maintaining a class as easy as maintaining an in memory database (provided that the dataset under test is consistent), and probably easier to debug.

You could back up that class with DBUnit, where you take a snapshot of your result set with dbunit, and have dbunit read it back during the test from xml, and have your dummy result set read the data from dbunit's classes. This would be a reasonable approach if the data was mildly complex.

I would go for the in memory database if the classes were so coupled that they need to read data that was modified as part of the same test. Even then, I would consider using a copy of the real database until you managed to pull that dependency apart.

A simple proxy generation method:

private static class SimpleInvocationHandler implements InvocationHandler {
    private Object invokee;

    public SimpleInvocationHandler(Object invokee) {
        this.invokee = invokee;
    }

    public Object invoke(Object proxy, Method method, Object[] args)
            throws Throwable {
        method = invokee.getClass().getMethod(method.getName(), method.getParameterTypes());
        if (!method.isAccessible()) {
            method.setAccessible(true);
        }
        try {
            return method.invoke(invokee, args);
        } catch (InvocationTargetException e) {
            throw e.getTargetException();
        }
    }
}

public static <T> T generateProxy(Object realObject, Class... interfaces) {
    return (T) Proxy.newProxyInstance(realObject.getClass().getClassLoader(), interfaces, new SimpleInvocationHandler(realObject));
}