Add unit test for asynchronous browse

scm-test/src/main/java/sonia/scm/repository/spi/SyncAsyncExecutors.java

@@ -1,7 +1,12 @@
 package sonia.scm.repository.spi;
 
+import java.io.Closeable;
+import java.util.concurrent.Executor;
+import java.util.concurrent.Executors;
+import java.util.concurrent.Semaphore;
 import java.util.function.Consumer;
 
+import static sonia.scm.repository.spi.SyncAsyncExecutor.ExecutionType.ASYNCHRONOUS;
 import static sonia.scm.repository.spi.SyncAsyncExecutor.ExecutionType.SYNCHRONOUS;
 
 public final class SyncAsyncExecutors {
@@ -20,4 +25,70 @@ public final class SyncAsyncExecutors {
       }
     };
   }
+
+  public static SyncAsyncExecutor asynchronousExecutor() {
+
+    Executor executor = Executors.newSingleThreadExecutor();
+
+    return new SyncAsyncExecutor() {
+      @Override
+      public ExecutionType execute(Consumer<ExecutionType> runnable) {
+        executor.execute(() -> runnable.accept(ASYNCHRONOUS));
+        return ASYNCHRONOUS;
+      }
+
+      @Override
+      public boolean hasExecutedAllSynchronously() {
+        return true;
+      }
+    };
+  }
+
+  public static AsyncExecutorStepper stepperAsynchronousExecutor() {
+
+    Executor executor = Executors.newSingleThreadExecutor();
+    Semaphore enterSemaphore = new Semaphore(0);
+    Semaphore exitSemaphore = new Semaphore(0);
+
+    return new AsyncExecutorStepper() {
+      @Override
+      public void close() {
+        enterSemaphore.release(Integer.MAX_VALUE);
+        exitSemaphore.release(Integer.MAX_VALUE);
+      }
+
+      @Override
+      public ExecutionType execute(Consumer<ExecutionType> runnable) {
+        executor.execute(() -> {
+          try {
+            enterSemaphore.acquire();
+          } catch (InterruptedException e) {
+            Thread.currentThread().interrupt();
+          }
+          runnable.accept(ASYNCHRONOUS);
+          exitSemaphore.release();
+        });
+        return ASYNCHRONOUS;
+      }
+
+      @Override
+      public void next() {
+        enterSemaphore.release();
+        try {
+          exitSemaphore.acquire();
+        } catch (InterruptedException e) {
+          Thread.currentThread().interrupt();
+        }
+      }
+
+      @Override
+      public boolean hasExecutedAllSynchronously() {
+        return true;
+      }
+    };
+  }
+
+  public interface AsyncExecutorStepper extends SyncAsyncExecutor, Closeable {
+    void next();
+  }
 }