public CompletableFuture<Void> stop() {
        final Server server = this.server.getAndSet(null);
        if (server == null || server.activePorts().isEmpty()) {
            return UnmodifiableFuture.completedFuture(null);
        }

        return server.stop();
    }
Stops the {@link Server} asynchronously.

@return the {@link CompletableFuture} that will complete when the {@link Server} is stopped.
junit5/src/main/java/com/linecorp/armeria/internal/testing/ServerRuleDelegate.java