No tests are displayed here:
https://ci.blueocean.io/blue/organizations/jenkins/jenkins-design-language/detail/topic%2Fadd-test-reports/2/tests/

However there are JUnit tests on the job in classic:
https://ci.blueocean.io/job/jenkins-design-language/job/topic%252Fadd-test-reports/lastCompletedBuild/testReport/PhantomJS_2_1_1_(Linux_0_0_0)/

At closer inspection it looks like the REST URL 404s https://ci.blueocean.io/blue/rest/organizations/jenkins/pipelines/jenkins-design-language/branches/topic%2Fadd-test-reports/runs/2/testReport/result