pkg/mock updating unittest dependency

pkg/pkg.status

 # Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 # Don't run any test-like files that show up in packages directories. It
 # shouldn't be necessary to run "pub install" in these packages, but if you do
 # it shouldn't break the tests.
 */packages/*/*: Skip
 */*/packages/*/*: Skip
 */*/*/packages/*/*: Skip
@@ skipping 323 matching lines @@
 
 [ $unchecked ]
 third_party/angular_tests/browser_test/angular: Skip # Requires checked mode.
 third_party/angular_tests/browser_test/core/scope: Skip # Requires checked mode.
 third_party/angular_tests/browser_test/core/zone: Skip # Requires checked mode.
 third_party/angular_tests/browser_test/directive/ng_repeat: Skip # Issue 17152
 third_party/angular_tests/browser_test/change_detection/dirty_checking_change_detector: Skip # Issue 17152
 
 [ $use_repository_packages ]
 analyzer/test/*: PubGetError
-mock/test/*: PubGetError # Issue 18735
 
 [ $runtime == ie9 ]
 polymer: Pass, Fail, Timeout # Issue 16717
 
 # No typed_data on IE9.
 http/test/html/client_test: Fail
 http/test/html/streamed_request_test: Skip
 http/test/mock_client_test: Fail
 http/test/multipart_test: Fail
 http/test/request_test: Fail
 http/test/response_test: Fail
 oauth2/test/authorization_code_grant_test: Fail
 oauth2/test/client_test: Fail
 oauth2/test/credentials_test: Fail
 oauth2/test/handle_access_token_response_test: Fail
 
 [ $runtime == drt ]
 http/test/html/client_test: Skip # Issue 18566