reactor-core/src/main/java/reactor/core/publisher/Hooks.java
static final Map<String, Function<? super Publisher<Object>, ? extends Publisher<Object>>> getOnEachOperatorHooks() {
		return Collections.unmodifiableMap(onEachOperatorHooks);
	}
static final Map<String, Function<? super Publisher<Object>, ? extends Publisher<Object>>> getOnEachOperatorHooks() {
		return Collections.unmodifiableMap(onEachOperatorHooks);
	}
Immutable views on hook trackers, for testing purpose