default Map<String, SamplingTestPlugin> flatten() {
        Map<String, SamplingTestPlugin> out = new HashMap<>();
        Map<String, SamplingTestPlugin> otherSamples = otherSamples();
        if (otherSamples != null) {
            for (Entry<String, SamplingTestPlugin> child : otherSamples.entrySet()) {
                for (Entry<String, SamplingTestPlugin> flattened : child.getValue().flatten().entrySet()) {
                    String key = child.getKey();
                    if (!flattened.getKey().isEmpty()) {
                        key += "." + flattened.getKey();
                    }
                    out.put(key, flattened.getValue());
                }
            }
        }
        out.put("", this);
        return out;
    }
@return a flattened list of child samples including this entry keyed as "this"
connect/runtime/src/test/java/org/apache/kafka/connect/runtime/isolation/SamplingTestPlugin.java