transport/server/play-server/src/main/java/play/server/Server.java
public static Server forRouter(Mode mode, Function<BuiltInComponents, Router> block) {
    return forRouter(mode, 0, block);
  }
public static Server forRouter(Mode mode, Function<BuiltInComponents, Router> block) {
    return forRouter(mode, 0, block);
  }
Create a server for the given router.

<p>The server will be running on a randomly selected ephemeral port, which can be checked using
the httpPort property.

<p>The server will be running in TEST mode.

@param mode The mode the server will run on.
@param block The block that creates the router.
@return The running server.