public TestReport mergedWith(TestReport other) {
        synchronized (monitor) {
            synchronized (other.monitor) {
                if (current != null || other.current != null)
                    throw new IllegalArgumentException("can only merge completed test reports");

                if (root.start().isAfter(other.root.start()))
                    throw new IllegalArgumentException("appended test report cannot have started before the one appended to");

                ContainerNode newRoot = new ContainerNode(null, null, root.name(), root.start());
                newRoot.children.addAll(root.children);
                newRoot.children.addAll(other.root.children);
                TestReport merged = new TestReport(clock, suite, newRoot);
                merged.complete();
                return merged;
            }
        }
    }
Verify the path from the root to the current node corresponds to the given id.
vespa-osgi-testrunner/src/main/java/com/yahoo/vespa/testrunner/TestReport.java