### Question:
FileDownloadService { String getContentFileNameWithoutExt() { assert contentFileNameWithoutExt != null; return new StringBuilder() .append(getCurrentTimeStamp()).append("_").append(contentFileNameWithoutExt).append("_backup") .toString(); } FileDownloadService(ContentKeeper content, FileDownloader fileDownloader, String contentFileNameWithoutExt); void performFileDownload();  }### Answer:
@Test public void filenameIsFormedWithTimestampAndBackupWord() { sut = new FileDownloadService(mockContentKeeper, mockFileDownloader, "jtalks"); String actualFilename = sut.getContentFileNameWithoutExt(); assertTrue(actualFilename.matches(getFileNameRegExp()), "Filename does not fit in the expected " + "format: YYYY-MM-DD_HH-MM-SS_jtalks_backup. Actual filename: " + actualFilename + "."); }