Put testsuite in its own directory

testsuite/classes/java/MultiThreading.java

@@ -0,0 +1,22 @@
+import java.util.concurrent.Executors;
+import java.util.stream.IntStream;
+import java.util.concurrent.TimeUnit;
+
+public class MultiThreading {
+    private int number = 0;
+
+    public static void main(String[] args) throws InterruptedException {
+        final var multiThreading = new MultiThreading();
+
+        final var service = Executors.newFixedThreadPool(3);
+        IntStream.range(0, 1000)
+            .forEach(count -> service.submit(multiThreading::increment));
+        service.awaitTermination(1000, TimeUnit.MILLISECONDS);
+
+        System.out.println(multiThreading.number);
+    }
+
+    public synchronized void increment() {
+        number += 1;
+    }
+}