add Periodic test

app/src/test/java/org/astraea/cost/PeriodicTest.java

@@ -0,0 +1,37 @@
+package org.astraea.cost;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.concurrent.TimeUnit;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+public class PeriodicTest extends Periodic<Map<Integer, Double>> {
+  private double brokerValue = 0.0;
+
+  @Test
+  void testTryUpdate() {
+    var broker1 = tryUpdate(this::testMap);
+    Assertions.assertEquals(broker1.get(0), 0.0);
+    var broker2 = tryUpdate(this::testMap);
+    Assertions.assertEquals(broker2.get(0), 0.0);
+    sleep(1);
+    broker2 = tryUpdate(this::testMap);
+    Assertions.assertEquals(broker2.get(0), 1.0);
+  }
+
+  Map<Integer, Double> testMap() {
+    var broker = new HashMap<Integer, Double>();
+    broker.put(0, brokerValue);
+    brokerValue++;
+    return broker;
+  }
+
+  private static void sleep(int seconds) {
+    try {
+      TimeUnit.SECONDS.sleep(seconds);
+    } catch (InterruptedException e) {
+      throw new RuntimeException(e);
+    }
+  }
+}