### Question:
DefaultWikiDescriptorDocumentHelper implements WikiDescriptorDocumentHelper { @Override public String getWikiIdFromDocumentFullname(String descriptorDocumentFullname) { return StringUtils.removeStart(descriptorDocumentFullname, "XWiki.XWikiServer").toLowerCase(); }  @Override DocumentReference getDocumentReferenceFromId(String wikiId); @Override String getWikiIdFromDocumentReference(DocumentReference descriptorDocumentReference); @Override String getWikiIdFromDocumentFullname(String descriptorDocumentFullname); @Override XWikiDocument getDocumentFromWikiId(String wikiId); @Override DocumentReference findXWikiServerClassDocumentReference(String wikiAlias); @Override XWikiDocument findXWikiServerClassDocument(String wikiAlias); @Override List<XWikiDocument> getAllXWikiServerClassDocument(); @Override List<String> getAllXWikiServerClassDocumentNames();  }### Answer:
@Test public void getWikiIdFromDocumentFullname() throws Exception { String result = mocker.getComponentUnderTest().getWikiIdFromDocumentFullname("XWiki.XWikiServerSubwiki"); assertEquals("subwiki", result); result = mocker.getComponentUnderTest().getWikiIdFromDocumentFullname("XWiki.XWikiServerXWikiServer"); assertEquals("xwikiserver", result); result = mocker.getComponentUnderTest().getWikiIdFromDocumentFullname("XWiki.XWikiServerAbbc"); assertEquals("abbc", result); }