trying to fix some stringex tests

Change-Id: Ifcf20a8f6fa5bcd187eead1679e380587d9e8e13
Reviewed-on: https://gerrit.instructure.com/29502
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Stephan Hagemann <stephan@pivotallabs.com>
Product-Review: Stephan Hagemann <stephan@pivotallabs.com>
QA-Review: Stephan Hagemann <stephan@pivotallabs.com>