Using Reflection in Unit Tests II

A couple of days ago, I blogged about the pros and cons of using Reflection in unit tests. Thanks to Samuel, who gave me a pointer to "PowerMock", I don't have to deal with the Reflection API anymore.

PowerMock is a Java framework that allows you to unit test code normally regarded as untestable.

To be more precise, PowerMock takes away the annoyance of dealing with the Reflection API. In case of the example presented in my previous post, instead of this code:

@Test
public void test_Calculate_Quote() throws Exception {
    Contract classUnderTest = new Contract(1L);
    Method calcMethod = getMethodOfClass(Contract.class, "calculateQuote");
    BigDecimal quote = (BigDecimal) calcMethod.invoke(classUnderTest, new DateMidnight(1982, 4, 27));
    assertEquals(new BigDecimal("7.79"), quote.setScale(2, RoundingMode.FLOOR));
}

private Method getMethodOfClass(Class argClass, String argMethodName) {
    Method[] methods = argClass.getDeclaredMethods();
    for (Method method : methods) {
        if (method.getName().equals(argMethodName)) {
            method.setAccessible(true);
            return method;
        }
    }
    throw new NoSuchMethodError("couldn't find " + argMethodName + " on class " + argClass);
}

you simply write this:

@Test
public void test_Calculate_Quote() throws Exception {
    Contract classUnderTest = new Contract(1L);
    BigDecimal quote = (BigDecimal) Whitebox.invokeMethod(classUnderTest, "calculateQuote", new DateMidnight(1982, 4, 27));
    assertEquals(new BigDecimal("7.79"), quote.setScale(2, RoundingMode.FLOOR));
}

I like the approach of hiding the complexity of the Reflection API behind an abstraction and in case of Whitebox it's even named perfectly. But accessing private methods is not the only thing PowerMock lets you do. In addition to much more you can set private fields, invoke hidden constructors and mock static methods. A feature that I really like is mocking final classes or methods, it can be quite helpful, when you are dealing with JDK classes like java.io.File.

I think PowerMock is a great extention to EasyMock and it should go into every developer's tool box. It's definitely going straight into mine.