### Question:
Utils { public static String differenceStrings(String str1, String str2) { if (str1 == null) return str2; if (str2 == null) return str1; int at = indexOfDifferenceStrings(str1, str2); if (at == INDEX_NOT_FOUND) return ""; return str2.substring(at); }  static float clamp(float min, float max, float value); static float getViewRawY(View view); static void setTint(Context context, CheckBox box, int color); static String getDate(@NonNull Context c, long f); @SuppressWarnings("deprecation") static int getColor(Context c, @ColorRes int color); static int dpToPx(Context c, int dp); static String differenceStrings(String str1, String str2); static void disableScreenRotation(@NonNull Activity activity); static void enableScreenRotation(@NonNull Activity activity); static boolean isDeviceInLandScape(Activity activity); static String sanitizeInput(String input); static Uri getUriForBaseFile(
      @NonNull Context context, @NonNull HybridFileParcelable baseFile); static int nthToLastCharIndex(int elementNumber, String str, char element); static String formatTimer(long timerInSeconds); @TargetApi(Build.VERSION_CODES.N) static File getVolumeDirectory(StorageVolume volume); static boolean isNullOrEmpty(final Collection<?> list); static boolean isNullOrEmpty(final String string); static void invalidateFab(
      MainActivity mainActivity, @Nullable Runnable callback, boolean open); static Snackbar showThemedSnackbar(
      MainActivity mainActivity,
      CharSequence text,
      int length,
      @StringRes int actionTextId,
      Runnable actionCallback);  }### Answer:
@Test public void testDifferenceStrings() { assertNull(Utils.differenceStrings(null, null)); assertEquals("abc", Utils.differenceStrings("abc", null)); assertEquals("abc", Utils.differenceStrings(null, "abc")); assertEquals("", Utils.differenceStrings("abc12345", "abc")); assertEquals("", Utils.differenceStrings("pqrstuv345", "pqrstuv")); assertEquals("12345", Utils.differenceStrings("abc", "abc12345")); }