Parameterized JUnit for SoftServe IT Academy

Math.java

public class Math {

    public static int pow(int number, int exponent) {
        return (int) java.lang.Math.pow(number, exponent); //just for lazy men ^_^
    }

    public static double mean(double... data) {
        double sum = 0;
        int length = data.length;
        for (int i = 0; i < length; i++) {
            sum += data[i];
        }
        return sum / length;
    }
}

MathTest.java

import org.junit.Assert;
import org.junit.Test;
import org.junit.experimental.runners.Enclosed;
import org.junit.runner.RunWith;
import org.junit.runners.Parameterized;

import java.util.Arrays;
import java.util.HashSet;

/**
 * @author Oleksandr Khomenko
 */
@RunWith(Enclosed.class) //Tell JUnit that "he" have to run static inner tests
public class MathTest {

    @RunWith(Parameterized.class)
    public static class PowTest {

        @Parameterized.Parameter
        public int number;                 //should be public
        @Parameterized.Parameter(1)
        public int exponenta;              //should be public
        @Parameterized.Parameter(2)
        public int expected;               //should be public

        @Parameterized.Parameters
        public static Iterable data() {    //should be public static
            Object[] first = {2, 2, 4};
            Object[] second = {3, 3, 27};
            Object[] third = {3, 13, 1594323};
            Object[][] objects = {         //an Array with Arrays. Included array should contain as many elements as parameters
                    first,
                    second,
                    third
            };
            return Arrays.asList(          //Iterable with Array. Thanks Java varags.... It eat one dimension from array above. Look at method signature of .asList()
                    objects                //And we have a List of one dimensional arrays.
            );
        }

        @Test
        public void pow() {               //Can contain more than one test, just add new method below
            int actual = Math.pow(this.number, this.exponenta);

            Assert.assertEquals(this.expected, actual);
        }
    }

    @RunWith(Parameterized.class)
    public static class MeanTest {

        @Parameterized.Parameter
        public double a;
        @Parameterized.Parameter(1)
        public double b;
        @Parameterized.Parameter(2)
        public double c;
        @Parameterized.Parameter(3)
        public double e;
        @Parameterized.Parameter(4)
        public double f;
        @Parameterized.Parameter(5)
        public double x;
        @Parameterized.Parameter(6)
        public double expected;

        @Parameterized.Parameters
        public static Iterable data() {
            HashSet<Object> data = new HashSet<>();
            data.add(Arrays.asList(1, 1, 1, 1, 1, 1, 1).toArray());
            data.add(Arrays.asList(6, 0, 0, 0, 0, 0, 1).toArray());
            data.add(Arrays.asList(1, 2, 3, 1, 2, 3, 2).toArray());
            return data;

        }

        @Test
        public void mean() {
            double actual = Math.mean(a,b,c,e,f,x);

            double delta = 0.01;
            Assert.assertEquals(this.expected, actual, delta);
        }
    }
}