add fray example.

integration-tests/src/main/java/example/FrayExample.java

@@ -0,0 +1,25 @@
+package example;
+import java.util.concurrent.atomic.AtomicInteger;
+
+public class FrayExample extends Thread {
+    static Object o = new Object();
+    static AtomicInteger a = new AtomicInteger();
+    static volatile int b;
+    public void run() {
+        int x = a.getAndIncrement();
+        synchronized(o) { // monitorenter
+            if (x == 0) {
+                try { o.wait(); } catch (InterruptedException ignore) { }
+            } else {
+                o.notify();
+            }
+        } // monitorexit
+        b = x;
+    }
+    public static void main(String[] args) throws Exception {
+        FrayExample[] threads = {new FrayExample(), new FrayExample()};
+        for (var thread : threads) thread.start();
+        for (var thread : threads) thread.join();
+        assert(b == 1);
+    }
+}

integration-tests/src/test/java/cmu/pasta/fray/it/core/FrayExampleTest.java

@@ -0,0 +1,26 @@
+package cmu.pasta.fray.it.core;
+
+import cmu.pasta.fray.core.scheduler.POSScheduler;
+import cmu.pasta.fray.it.IntegrationTestRunner;
+import example.FrayExample;
+import org.junit.jupiter.api.Test;
+
+import java.util.Random;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+public class FrayExampleTest extends IntegrationTestRunner {
+
+    @Test
+    void test() {
+        String result = runTest(() -> {
+            try {
+                FrayExample.main(new String[0]);
+            } catch (Exception e) {
+                throw new RuntimeException(e);
+            }
+            return null;
+        }, new POSScheduler(new Random()), 10000);
+        assertTrue(result.contains("DeadlockException") || result.contains("AssertionError"));
+    }
+}