Add failFollowup

Signed-off-by: TheMode <themode@outlook.fr>

src/test/java/net/minestom/server/api/EnvImpl.java

@@ -12,6 +12,7 @@ import java.util.concurrent.CopyOnWriteArrayList;
 import java.util.function.Consumer;
 
 import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.fail;
 
 final class EnvImpl implements Env {
     private final ServerProcess process;
@@ -80,7 +81,17 @@ final class EnvImpl implements Env {
         }
 
         @Override
-        public void setHandler(@NotNull Consumer<E> handler) {
+        public void followup(@NotNull Consumer<E> handler) {
+            updateHandler(handler);
+        }
+
+        @Override
+        public void failFollowup() {
+            updateHandler(e -> fail("Event " + e.getClass().getSimpleName() + " was not expected"));
+        }
+
+        void updateHandler(@NotNull Consumer<E> handler) {
+            check();
             this.initialized = true;
             this.called = false;
             this.handler = e -> {
@@ -89,12 +100,6 @@ final class EnvImpl implements Env {
             };
         }
 
-        @Override
-        public void followup(@NotNull Consumer<E> handler) {
-            check();
-            setHandler(handler);
-        }
-
         void check() {
             assertTrue(!initialized || called, "Last listener has not been called: " + eventType.getSimpleName());
         }

src/test/java/net/minestom/server/api/FlexibleListener.java

@@ -6,11 +6,13 @@ import org.jetbrains.annotations.NotNull;
 import java.util.function.Consumer;
 
 public interface FlexibleListener<E extends Event> {
-
-    void setHandler(@NotNull Consumer<E> handler);
-
     /**
      * Updates the handler. Fails if the previous followup has not been called.
      */
     void followup(@NotNull Consumer<E> handler);
+
+    /**
+     * Fails if an event is received. Valid until the next followup call.
+     */
+    void failFollowup();
 }