gwt-test-utils indeed seems to support Storage
: https://github.com/gwt-test-utils/gwt-test-utils/blob/master/gwt-test-utils/src/test/java/com/googlecode/gwt/test/StorageTest.java
…or you could just use a GWTTestCase
; this is how the feature is tested in GWT itself. GWT 2.6 has upgraded its HtmlUnit dependency which should now support local/session storage (I suppose); otherwise you could launch your tests in a real browser: http://www.gwtproject.org/doc/latest/DevGuideTestingRemoteTesting.html