This is a testharness.js-based test.
FAIL .flexbox 1 assert_equals: 
<div class="flexbox column-wrap">
       <div>
            <span data-expected-height="50"></span>
        </div>
        <div>
            <span data-expected-height="50"></span>
        </div>
    </div>
height expected 50 but got 0
FAIL .flexbox 2 assert_equals: 
<div class="flexbox column">
        <div>
            <span data-expected-height="100"></span>
        </div>
    </div>
height expected 100 but got 0
Harness: the test ran to completion.