### Question:
HashPathIdMapper implements IdMapper { public URI getExternalId(URI internalId) throws NullPointerException { String fullPath = internalId.toString().substring( internalScheme.length() + 1); int i = fullPath.lastIndexOf('/'); String encodedURI; if (i == -1) encodedURI = fullPath; else encodedURI = fullPath.substring(i + 1); return URI.create(decode(encodedURI)); } HashPathIdMapper(String pattern); URI getExternalId(URI internalId); URI getInternalId(URI externalId); String getInternalPrefix(String externalPrefix);  }### Answer:
@Test public void testGetExternalId() { IdMapper mapper = new HashPathIdMapper("##/##/##"); assertEquals(URI1, mapper.getExternalId(URI1_ENCODED)); assertEquals(URI2, mapper.getExternalId(URI2_ENCODED)); assertEquals(URI3, mapper.getExternalId(URI3_ENCODED)); }