### Question:
WalletUtils { public static String getDefaultKeyDirectory() { return getDefaultKeyDirectory(System.getProperty("os.name")); }  static String generateFullNewWalletFile(String password, File destinationDirectory); static String generateLightNewWalletFile(String password, File destinationDirectory); static String generateNewWalletFile(
            String password, File destinationDirectory, boolean useFullScrypt); static String generateWalletFile(
            String password, ECKeyPair ecKeyPair, File destinationDirectory, boolean useFullScrypt); static Bip39Wallet generateBip39Wallet(String password, File destinationDirectory); static Credentials loadCredentials(String password, String source); static Credentials loadCredentials(String password, File source); static Credentials loadBip39Credentials(String password, String mnemonic); static String getDefaultKeyDirectory(); static String getTestnetKeyDirectory(); static String getMainnetKeyDirectory(); static boolean isValidPrivateKey(String privateKey); static boolean isValidAddress(String input);  }### Answer:
@Test public void testGetDefaultKeyDirectory() { assertTrue(WalletUtils.getDefaultKeyDirectory("Mac OS X") .endsWith(String.format("%sLibrary%sEthereum", File.separator, File.separator))); assertTrue(WalletUtils.getDefaultKeyDirectory("Windows") .endsWith(String.format("%sEthereum", File.separator))); assertTrue(WalletUtils.getDefaultKeyDirectory("Linux") .endsWith(String.format("%s.ethereum", File.separator))); }