### Question:
AS2IOHelper { @Nullable public static String getFilenameFromMessageID (@Nonnull final String sMessageID) { String s = StringHelper.removeAll (sMessageID, '<'); s = StringHelper.removeAll (s, '>'); return FilenameHelper.getAsSecureValidASCIIFilename (s); } private  AS2IOHelper(); @Nonnull static FileOperationManager getFileOperationManager(); @Nonnull static File getDirectoryFile(@Nonnull final String sDirectory); @Nonnull @Nonempty static String getTransferRate(final long nBytes, @Nonnull final StopWatch aSW); @Nonnull static File getUniqueFile(@Nonnull final File aDir, @Nullable final String sFilename); static void handleError(@Nonnull final File aFile, @Nonnull final String sErrorDirectory); @Nonnull static File moveFile(@Nonnull final File aSrc,
                               @Nonnull final File aDestFile,
                               final boolean bOverwrite,
                               final boolean bRename); @Nullable static String getFilenameFromMessageID(@Nonnull final String sMessageID); @Nullable static String getSafeFileAndFolderName(@Nullable final String s); @Nonnull @ReturnsMutableCopy static byte [] getAllAsciiBytes(@Nonnull final String sString); @Nonnull static OutputStream getContentTransferEncodingAwareOutputStream(@Nonnull final OutputStream aOS,
                                                                          @Nullable final String sEncoding); @Nonnull static InputStream getContentTransferEncodingAwareInputStream(@Nonnull final InputStream aIS,
                                                                        @Nullable final String sEncoding);  }### Answer:
@Test public void testGetFilenameFromMessageID () { assertNull (AS2IOHelper.getFilenameFromMessageID ("")); assertNull (AS2IOHelper.getFilenameFromMessageID ("<<<<>>>>")); assertEquals ("a", AS2IOHelper.getFilenameFromMessageID ("a")); assertEquals ("a", AS2IOHelper.getFilenameFromMessageID ("<a>")); assertEquals ("a", AS2IOHelper.getFilenameFromMessageID ("<<<<<a>>>>>")); assertEquals ("a@b.c", AS2IOHelper.getFilenameFromMessageID ("<<<<<a@b.c>>>>>")); }