public InetSocketAddress socketAddress(SessionProtocol protocol) {
        requireNonNull(protocol, "protocol");
        ensureStarted();
        return new InetSocketAddress("127.0.0.1", port(protocol));
    }
Returns the {@link InetSocketAddress} of the specified {@link SessionProtocol} for the {@link Server}.

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