Apparently a name is needed.

.circleci/config.yml

@@ -29,6 +29,7 @@ jobs:
             - ~/.gradle/caches
           key: v1-gradle-cache-{{ checksum "build.gradle" }}
       - run:
+          name: Prepare test output
           command: |
             mkdir -p ~/test-results/junit/
             find . -type f -regex ".*/build/test-results/.*xml" -exec cp {} ~/test-results/junit/ \;