public Endpoint endpoint(SessionProtocol protocol) {
        ensureStarted();
        return Endpoint.unsafeCreate("127.0.0.1", port(protocol));
    }
Returns the {@link Endpoint} of the specified {@link SessionProtocol} for the {@link Server}.

@throws IllegalStateException if the {@link Server} is not started or
                              it did not open the port for the specified {@link SessionProtocol}.
junit5/src/main/java/com/linecorp/armeria/internal/testing/ServerRuleDelegate.java