A file js-test-results.xml with result containing line breaks:

<testsuites name="jest tests">

  <testsuite name="ProductData" tests="1" errors="0" failures="1" skipped="0" timestamp="2017-06-21T10:19:58" time="1.518">

    <testcase classname="ProductData should return blabla" name="ProductData blabla" time="0.014">

      <failure message="Error: expect(a).toEqual(expected)

Expected value to equal:

  {"byId": {}, "tags": {}}

...

In Jenkins test results page it is displayed as one long line:

Error: expect(a).toEqual(expected) Expected value to equal: {"byId": {}, "tags": {}}