UnittestProto.optionalInt32Extension.getDescriptor();
assertEquals(extension, file.getExtensions().get(0));
assertEquals(extension,
file.findExtensionByName("optional_int32_extension"));
assertNull(file.findExtensionByName("no_such_ext"));
assertNull(file.findExtensionByName(
"protobuf_unittest.optional_int32_extension"));
assertEquals(Collections.emptyList(),
UnittestImport.getDescriptor().getExtensions());
for (int i = 0; i < file.getExtensions().size(); i++) {
assertEquals(i, file.getExtensions().get(i).getIndex());