### Question:
Tools { public static String emptyIfNull(@Nullable final String string) { if (string == null) { return ""; } return string; } private  Tools(); static String getTime(); static String getDoubleDigit(final int number); static String dateToString(@Nullable final Date d, final String format); static String decimalFormat(final String format, final double number); static boolean isValidNick(@Nullable final String nick); static String byteToString(final long bytes); static int getBytes(final String text); static void sleep(final long millis); @Nullable static String capitalizeFirstLetter(@Nullable final String word); @Nullable static String shorten(@Nullable final String word, final int length); @Nullable static String getFileExtension(@Nullable final String filename); @Nullable static String getFileBaseName(@Nullable final String filename); static double percent(final double fraction, final double total); static double percentOf(final double percent, final double total); static String postPadString(final String stringToPad, final int paddedLength); static boolean isEmpty(@Nullable final String string); static String appendSlash(final String path); static File getFileWithIncrementedName(final File existingFile); static String emptyIfNull(@Nullable final String string);  }### Answer:
@Test public void emptyIfNullShouldReturnAnEmptyStringWhenInputIsNull() { assertEquals("", Tools.emptyIfNull(null)); }
@Test public void emptyIfNullShouldReturnAnEmptyStringWhenInputIsEmpty() { assertEquals("", Tools.emptyIfNull("")); }
@Test public void emptyIfNullShouldReturnTheInputStringWhenInputIsNotEmpty() { assertEquals("hello", Tools.emptyIfNull("hello")); }