### Question:
HashPathIdMapper implements IdMapper { public URI getInternalId(URI externalId) throws NullPointerException { if (externalId == null) { throw new NullPointerException(); } String uri = externalId.toString(); StringBuilder buffer = new StringBuilder(uri.length() + 16); buffer.append(internalScheme + ":"); getPath(uri, buffer); encode(uri, buffer); return URI.create(buffer.toString()); } HashPathIdMapper(String pattern); URI getExternalId(URI internalId); URI getInternalId(URI externalId); String getInternalPrefix(String externalPrefix);  }### Answer:
@Test public void testGetInternalId() { IdMapper mapper = new HashPathIdMapper("##/##/##"); assertEquals(URI1_ENCODED, mapper.getInternalId(URI1)); assertEquals(URI2_ENCODED, mapper.getInternalId(URI2)); assertEquals(URI3_ENCODED, mapper.getInternalId(URI3)); }