function _setupTestEnvironment(testDocument, testPreferences) {
        isPrefHintsEnabled = _isPrefDocument(testDocument);
        data = testPreferences;
    }
@private

`isPrefHintsEnabled` must be set to true to allow code hints

It also loads a set of preferences that we need for running unit tests, this
will not break unit tests in case we add new preferences in the future.

@param {!Document} testDocument
@param {!Object} testPreferences