### Question:
Library { public static String reverse(String s) { return new StringBuilder(s).reverse().toString(); }  static String reverse(String s); static boolean isPalindrome(String s); static boolean isPalindrome(int x); static int sqrt(int x); static long sqrt(long x); static BigInteger sqrt(BigInteger x); static boolean isSquare(int x); static int pow(int x, int y); static int powMod(int x, int y, int m); static int reciprocalMod(int x, int m); static BigInteger factorial(int n); static BigInteger binomial(int n, int k); static int gcd(int x, int y); static boolean isPrime(int x); static boolean[] listPrimality(int n); static int[] listPrimes(int n); static int[] listSmallestPrimeFactors(int n); static int totient(int n); static int[] listTotients(int n); static boolean nextPermutation(int[] arr);  }### Answer:
@Test public void testReverse() { assertEquals("", Library.reverse("")); assertEquals("a", Library.reverse("a")); assertEquals("ba", Library.reverse("ab")); assertEquals("001", Library.reverse("100")); assertEquals("a0a", Library.reverse("a0a")); }