### Question:
Base64 extends BaseNCodec { public static boolean isBase64(final byte octet) { return octet == PAD_DEFAULT || (octet >= 0 && octet < DECODE_TABLE.length && DECODE_TABLE[octet] != -1); } Base64();  Base64(final boolean urlSafe);  Base64(final int lineLength);  Base64(final int lineLength, final byte[] lineSeparator);  Base64(final int lineLength, final byte[] lineSeparator, final boolean urlSafe); boolean isUrlSafe(); @Deprecated static boolean isArrayByteBase64(final byte[] arrayOctet); static boolean isBase64(final byte octet); static boolean isBase64(final String base64); static boolean isBase64(final byte[] arrayOctet); static byte[] encodeBase64(final byte[] binaryData); static String encodeBase64String(final byte[] binaryData); static byte[] encodeBase64URLSafe(final byte[] binaryData); static String encodeBase64URLSafeString(final byte[] binaryData); static byte[] encodeBase64Chunked(final byte[] binaryData); static byte[] encodeBase64(final byte[] binaryData, final boolean isChunked); static byte[] encodeBase64(final byte[] binaryData, final boolean isChunked, final boolean urlSafe); static byte[] encodeBase64(final byte[] binaryData, final boolean isChunked,
                                      final boolean urlSafe, final int maxResultSize); static byte[] decodeBase64(final String base64String); static byte[] decodeBase64(final byte[] base64Data); static BigInteger decodeInteger(final byte[] pArray); static byte[] encodeInteger(final BigInteger bigInt);  }### Answer:
@Test public void testIsStringBase64() { final String nullString = null; final String emptyString = ""; final String validString = "abc===defg\n\r123456\r789\r\rABC\n\nDEF==GHI\r\nJKL=============="; final String invalidString = validString + (char)0; try { Base64.isBase64(nullString); fail("Base64.isStringBase64() should not be null-safe."); } catch (final NullPointerException npe) { assertNotNull("Base64.isStringBase64() should not be null-safe.", npe); } assertTrue("Base64.isStringBase64(empty-string) is true", Base64.isBase64(emptyString)); assertTrue("Base64.isStringBase64(valid-string) is true", Base64.isBase64(validString)); assertFalse("Base64.isStringBase64(invalid-string) is false", Base64.isBase64(invalidString)); }