Lab2.java contains the following code:   public final class Lab2 {       /**    * This is empty by design, Lab2 cannot be instantiated    */    private Lab2() {        // empty by design    }               /**    * Returns the sum of a consecutive set of numbers from start to end .    *    * @pre start and end are small enough to let this    * method return an int. This means the return value at most requires 4 bytes and    * no overflow would happen.    *    * @param start is an integer number    * @param end is an integer number    * @return the sum of start + (start + 1) + .... + end    */    public static int sum(int start, int end) {        //Insert your code here and change the return statement to fit your implementation.        return 0;    }    /**    * This method creates a string using the given char    * by repeating the character n times.    *    * @param first is the given character by which the string is made.    * @param n is the number of characters in the final string    * @return a string made of the given character.    *    * @pre n is not negative.    */    public static String makeString(char first, int n) {        //Insert your code here and change the return statement to fit your implementation.        return "";    }    /**    * This method gets two strings and interlace a string using the    * these two input strings. The number of words in the returned string is as much    * as the value of the third input parameter.    *    * @param first is the string that is used in the even position of the returned result [ asuming    * that the position starts from zero]    * @param second is the string that is used in the odd position of the returned result    * @param n is the number of words in the returned result.    * @return returns a string made of the first and the second input parameter.    */    public static String interlace(String first, String second, int n) {        //Insert your code here and change the return statement to fit your implementation.        return "";    }    /**    * This method returns a substring of the given input string that is enclosed in two    * given characters.    * @param str is a string that contains at least two characters including open and close    * @param open is a character at the beginning of the string that should be returned.    * @param close is a character at the end of the string that should be returned.    * @return returns a string enclosed in two given characters of open and close .    * @pre The given str contains only one open and one close character.    */    public static String getSubstring(String str, char open, char close) {        //Insert your code here and change the return statement to fit your implementation.        return "";    }       /**    * This method converts a decimal value into its binary representation.    * @param value is a positive integer number    * @return the binary representation of the input.    * @pre the input is a positive integer number.    */       public static String decimalToBinary(int value) {        //Insert your code here and change the return statement to fit your implementation.        return "";    } } Lab2Tester.java contains the following code:   public class Lab2Tester {       // sum       @Test    public void testSum1() {        int start = 0;        int end = 5;        int sum= 0;        for (int i = start ; i <= end ; i++)            sum += i;               assertEquals("Failed at sum (" + start + ", " + end + ")", sum, Lab2.sum(start, end));               }       @Test    public void testMakeString1() {        char init = '*';        int n = 5;        String result = "";        for (int i = 0 ; i < n ; i++)            result += init;        assertEquals("Failed at makeString(" + init + ", " + n + ")", result, Lab2.makeString(init, n));      }       @Test    public void testInterlace6() {        String str1 = "Hello ";        String str2 = "World ";        String result = "Hello World Hello World Hello ";        assertEquals("Failed: interlace(\"*\",\"-\",5)", result, Lab2.interlace("Hello ","World ",5));    }    @Test    public void testGetSubstring1() {        String str1 = "x + y + z - ( y * z) / 3 * n ";        String result = " y * z";        char open = '(';        char close = ')';        assertEquals("Failed: getSubstring(\"x + y + z - ( y * z) / 3 * n \", \"(\", \")\")", result, Lab2.getSubstring("x + y + z - ( y * z) / 3 * n ", '(', ')'));    }    @Test    public void testDecimalToBinary4() {        int decimal = 23;        String binary = "10111";        assertEquals("Failed: decimalToBinary(23)", binary, Lab2.decimalToBinary(23));    } }