Stupid test runner tricks - Permute all the orders your tests can run in

PermutationSpringTestRunner.java

package com.skylosian;

import static com.google.common.math.LongMath.factorial;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.LinkedList;
import java.util.List;
import java.util.Random;
import java.util.stream.LongStream;
import org.junit.runners.model.FrameworkMethod;
import org.junit.runners.model.InitializationError;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

public class PermuteRunner extends SpringJUnit4ClassRunner {

    private static Random rand;

    /**
     * Creates a BlockJUnit4ClassRunner to run {@code klass}
     *
     * @throws InitializationError if the test class is malformed.
     */
    public PermuteRunner(Class<?> klass) throws InitializationError {
        super(klass);
    }

    private static <T> List<T> permutationHelper(long no, LinkedList<T> in, List<T> out) {
        if (in.isEmpty()) {
            return out;
        }
        long subFactorial = factorial(in.size() - 1);
        out.add(in.remove((int) (no / subFactorial)));
        return permutationHelper(no % subFactorial, in, out);
    }

    protected List<FrameworkMethod> computeTestMethods() {
        List<FrameworkMethod> methods = super.computeTestMethods();
        rand = new Random();
        rand.setSeed(System.currentTimeMillis());
        List<FrameworkMethod> collector = new ArrayList();
        Arrays.stream(LongStream
            .range(1, factorial(methods.size()) - factorial(methods.size() - 1)).toArray())
            .forEach(
                number ->
                    permutationHelper(
                        number,
                        new LinkedList(methods),
                        collector)
            );
        return collector;
    }
}