public Server server() {
        final Server server = this.server.get();
        if (isStopped(server)) {
            throw new IllegalStateException("server did not start.");
        }
        assert server != null;
        return server;
    }
Returns the started {@link Server}.

@throws IllegalStateException if the {@link Server} is not started
junit5/src/main/java/com/linecorp/armeria/internal/testing/ServerRuleDelegate.java