Play framework 2.5.x: IllegalStateException: Attempted to call materialize () after closing ActorMaterializer

Question

The goal of the Play server is to act as an intermediate service for another system, where end users gain access to a small part of the functionality in a web browser on their smartphone.

The service functions as intended when connected to a real system. But I want to have unit tests in blackbox mode. Testing functionality from start to finish. In order not to rely on a real system where values ​​change every day, I wanted to use the same approach as in Service Testing and combine it with route testing, as shown in the test example, from play-java-seed , shown here for facilities:

public class HomeControllerTest extends WithApplication {

    @Override
    protected Application provideApplication() {
        return new GuiceApplicationBuilder().build();
    }

    @Test
    public void testIndex() {
        Http.RequestBuilder request = new Http.RequestBuilder()
                .method(GET)
                .uri("/");

        Result result = route(app, request);
        assertEquals(OK, result.status());
    }
}

:

package controllers;

import java.util.*;

import org.junit.*;
import static org.junit.Assert.*;

import play.Application;
import play.inject.guice.GuiceApplicationBuilder;
import play.mvc.Result;
import play.mvc.Http.RequestBuilder;
import play.routing.*;
import play.server.Server;
import play.test.WithApplication;
import static play.mvc.Http.Status.*;
import static play.mvc.Results.*;
import static play.test.Helpers.*;

public class ApplicationControllerTest extends WithApplication {
  static int FAKE_SERVICE_PORT = 7070;
  Server server;

  @Override
  protected Application provideApplication() {
    return new GuiceApplicationBuilder()
      .configure("externalSystem.port", FAKE_SERVICE_PORT)
      .configure("externalSystem.host", "localhost")
      .build();
  }

  @Before
  public void setup() {
    Router router = new RoutingDsl()
      .GET("/b/1/").routeTo(() ->
        // Request for branch information
        ok().sendResource("externalSystem/getBranch.json")
      )
      .GET("/b/1/a/19033/").routeTo(() ->
        // Request generating an already arrived appointment
        ok().sendResource("externalSystem/arrivedAppointment.json")
      )
      .GET("/b/1/a/19962/").routeTo(() ->
        // Request generating a newly created appointment
        ok().sendResource("externalSystem/createdAppointment.json")
      )
      .build();
    server = Server.forRouter(router, FAKE_SERVICE_PORT);
  }

  @After
  public void tearDown() throws Exception {
    server.stop();
  }

  @Test
  public void AppCtrl() throws Exception {
    // // These values are defined in the json files
    String customerName = "Test User";
    String branchName = "Test Branch";

    RequestBuilder request = new RequestBuilder().method(GET).uri("/1/19962");

    Result result = route(app, request);
    assertEquals(OK, result.status());
    assertTrue(contentAsString(result).contains(customerName));
    assertTrue(contentAsString(result).contains(branchName));
  }
}

sbt test IllegalStateException:

[error] Test controllers.ApplicationControllerTest.AppCtrl failed: java.lang.IllegalStateException: Attempted to call materialize() after the ActorMaterializer has been shut down., took 4.165 sec
[error]     at akka.stream.impl.ActorMaterializerImpl.materialize(ActorMaterializerImpl.scala:164)
[error]     at akka.stream.impl.ActorMaterializerImpl.materialize(ActorMaterializerImpl.scala:146)
[error]     at akka.stream.scaladsl.RunnableGraph.run(Flow.scala:350)
[error]     at play.api.libs.streams.DoneAccumulator.run(Accumulator.scala:161)
[error]     at play.api.test.EssentialActionCaller$class.call(Helpers.scala:225)
[error]     at play.api.test.Helpers$.call(Helpers.scala:382)
[error]     at play.api.test.RouteInvokers$class.route(Helpers.scala:247)
[error]     at play.api.test.Helpers$.route(Helpers.scala:382)
[error]     at play.api.test.RouteInvokers$class.jRoute(Helpers.scala:234)
[error]     at play.api.test.Helpers$.jRoute(Helpers.scala:382)
[error]     at play.api.test.Helpers.jRoute(Helpers.scala)
[error]     at play.test.Helpers.route(Helpers.java:360)
[error]     at play.test.Helpers.route(Helpers.java:355)
[error]     at controllers.ApplicationControllerTest.AppCtrl(ApplicationControllerTest.java:63)
[error]     ...
[error] Failed: Total 1, Failed 1, Errors 0, Passed 0
[error] Failed tests:
[error]         controllers.ApplicationControllerTest
[error] (test:test) sbt.TestsFailedException: Tests unsuccessful

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