Using Reflection for Testing

I am working on a presentation about the ‘Single Responsibility Principle’, based on my previous post.
It take most of my time.

In the meantime, I want to share a sample code of how I use to test inner fields in my classes.
I am doing it for a special case of testing, which is more of an integration test.
In the standard unit testing of the dependent class, I am using mocks of the dependencies.

One approach would be to wire everything and then run some kind of integration test of the logic.
I don’t want to do this. It will make the test hard to maintain.

The other approach is to check wiring directly.
And for that I am using reflection.

Below is a sample code of the testing method, and the usage.
Notice how I am catching the exception and throws a RuntimeException in case there is a problem.
This way, I have cleaner tested code.

	// Somewhere in a different utility class for testing
	@SuppressWarnings("unchecked")
	public static <T> T realObjectFromField(Class<?> clazz, String fieldName, Object object) {
	Field declaredField = accessibleField(clazz, fieldName);
	try {
	return (T) declaredField.get(object);
	} catch (IllegalArgumentException \| IllegalAccessException e) {
	throw new RuntimeException(e);
	}
	}

	private static Field accessibleField(Class<?> clazz, String fieldName) {
	try {
	Field declaredField = clazz.getDeclaredField(fieldName);
	declaredField.setAccessible(true);
	return declaredField;
	} catch (NoSuchFieldException \| SecurityException e) {
	throw new RuntimeException(e);
	}
	}


	// This is how we use it in a test method
	import static mypackage.ReflectionUtils.realObjectFromField;

	ItemFiltersMapperByFlag mapper = realObjectFromField(ItemsFilterExecutor.class, "filtersMapper", filterExecutor);
	assertNotNull("mapper is null. Check wiring", mapper);

view raw

realObjectFromField.java

hosted with ❤ by GitHub

Learning and Improving as a Craftsman Developer