make sure server port in test context is only defined once.

src/test/java/ch/ibw/appl/todo/server/functional/shared/FunctionalTest.java

@@ -11,11 +11,14 @@
 public class FunctionalTest {
 
   public static class TodoApplication implements SparkApplication {
-    private HttpServer httpServer;
+    private final HttpServer httpServer;
+
+    public TodoApplication(Integer port) {
+      httpServer = new HttpServer(String.valueOf(port), true);
+    }
 
     @Override
     public void init() {
-      httpServer = new HttpServer("4567", true);
       httpServer.start();
     }
 
@@ -26,7 +29,7 @@ public void destroy() {
   }
 
   @Rule
-  public SparkServer<TodoApplication> httpClient = new SparkServer<>(TodoApplication.class);
+  public SparkServer<TodoApplication> httpClient = new SparkServer<>(TodoApplication.class, 4567);
 
   public HttpResponse<String> executeGet(String path, String acceptType) {
     HttpRequest.Builder method = httpClient.get(path);

src/test/java/ch/ibw/appl/todo/server/functional/shared/SparkServer.java

@@ -3,7 +3,6 @@
 import org.junit.rules.ExternalResource;
 import org.junit.runner.Description;
 import org.junit.runners.model.Statement;
-import spark.Service;
 import spark.servlet.SparkApplication;
 
 import java.io.IOException;
@@ -17,17 +16,15 @@ public class SparkServer<T extends SparkApplication> extends ExternalResource {
   private final Class<T> sparkApplicationClass;
   private T sparkApplication;
   private final String protocolHostPort;
+  private int port;
   private final HttpClient httpClient;
   private final HttpRequest.Builder requestBuilder = HttpRequest.newBuilder();
 
-  SparkServer(Class<T> sparkApplicationClass) {
-    this(sparkApplicationClass, Service.SPARK_DEFAULT_PORT);
-  }
-
   SparkServer(Class<T> sparkApplicationClass, int port) {
     this.sparkApplicationClass = sparkApplicationClass;
     this.protocolHostPort = "http://localhost:" + port;
     this.httpClient = HttpClient.newHttpClient();
+    this.port = port;
   }
 
   @Override
@@ -37,7 +34,7 @@ public Statement apply(Statement base, Description description) {
 
   @Override
   protected void before() throws Throwable {
-    this.sparkApplication = this.sparkApplicationClass.getDeclaredConstructor().newInstance();
+    this.sparkApplication = this.sparkApplicationClass.getDeclaredConstructor(Integer.class).newInstance(port);
     this.sparkApplication.init();
   }