Fix flaky durations test
Fix flaky durations test

Unfortunately due to fluctuations in runtime "test_something"
might still appear in the final message.

Example failure:

https://ci.appveyor.com/project/pytestbot/pytest/builds/19494829/job/8lx847u0c78m63wf

RonnyPfannschmidt/pytest,nicoddemus/pytest,pfctdayelise/pytest,The-Compiler/pytest,pytest-dev/pytest,alfredodeza/pytest,markshao/pytest,tomviner/pytest,ddboline/pytest,Akasurde/pytest,hackebrot/pytest,nicoddemus/pytest,txomon/pytest,tomviner/pytest,The-Compiler/pytest