diff --git a/sentinel-cluster/sentinel-cluster-server-default/pom.xml b/sentinel-cluster/sentinel-cluster-server-default/pom.xml
index ed98f2add2..b222431b0e 100644
--- a/sentinel-cluster/sentinel-cluster-server-default/pom.xml
+++ b/sentinel-cluster/sentinel-cluster-server-default/pom.xml
@@ -41,7 +41,16 @@
             <artifactId>sentinel-datasource-nacos</artifactId>
             <scope>test</scope>
         </dependency>
-
+        <dependency>
+            <groupId>org.powermock</groupId>
+            <artifactId>powermock-module-junit4</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.powermock</groupId>
+            <artifactId>powermock-api-mockito2</artifactId>
+            <scope>test</scope>
+        </dependency>
         <dependency>
             <groupId>junit</groupId>
             <artifactId>junit</artifactId>
diff --git a/sentinel-cluster/sentinel-cluster-server-default/src/main/java/com/alibaba/csp/sentinel/cluster/flow/statistic/metric/ClusterParamMetric.java b/sentinel-cluster/sentinel-cluster-server-default/src/main/java/com/alibaba/csp/sentinel/cluster/flow/statistic/metric/ClusterParamMetric.java
index 12710e71af..20279b0589 100644
--- a/sentinel-cluster/sentinel-cluster-server-default/src/main/java/com/alibaba/csp/sentinel/cluster/flow/statistic/metric/ClusterParamMetric.java
+++ b/sentinel-cluster/sentinel-cluster-server-default/src/main/java/com/alibaba/csp/sentinel/cluster/flow/statistic/metric/ClusterParamMetric.java
@@ -15,20 +15,13 @@
  */
 package com.alibaba.csp.sentinel.cluster.flow.statistic.metric;
 
-import java.util.ArrayList;
-import java.util.Collections;
-import java.util.Comparator;
-import java.util.HashMap;
-import java.util.List;
-import java.util.Map;
-import java.util.Map.Entry;
-import java.util.Set;
-
-import com.alibaba.csp.sentinel.cluster.flow.statistic.data.ClusterFlowEvent;
 import com.alibaba.csp.sentinel.slots.statistic.base.LongAdder;
 import com.alibaba.csp.sentinel.slots.statistic.cache.CacheMap;
 import com.alibaba.csp.sentinel.util.AssertUtil;
 
+import java.util.*;
+import java.util.Map.Entry;
+
 /**
  * @author Eric Zhao
  * @since 1.4.0
@@ -89,6 +82,7 @@ public double getAvg(Object value) {
     }
 
     public Map<Object, Double> getTopValues(int number) {
+        AssertUtil.isTrue(number > 0, "number must be positive");
         metric.currentWindow();
         List<CacheMap<Object, LongAdder>> buckets = metric.values();
 
@@ -114,7 +108,7 @@ public Map<Object, Double> getTopValues(int number) {
             @Override
             public int compare(Entry<Object, Long> a,
                                Entry<Object, Long> b) {
-                return (int)(b.getValue() == null ? 0 : b.getValue()) - (int)(a.getValue() == null ? 0 : a.getValue());
+                return (int) (b.getValue() == null ? 0 : b.getValue()) - (int) (a.getValue() == null ? 0 : a.getValue());
             }
         });
 
@@ -126,7 +120,7 @@ public int compare(Entry<Object, Long> a,
             if (x.getValue() == 0) {
                 break;
             }
-            doubleResult.put(x.getKey(), ((double)x.getValue()) / metric.getIntervalInSecond());
+            doubleResult.put(x.getKey(), ((double) x.getValue()) / metric.getIntervalInSecond());
         }
 
         return doubleResult;
diff --git a/sentinel-cluster/sentinel-cluster-server-default/src/test/java/com/alibaba/csp/sentinel/cluster/flow/statistic/limit/GlobalRequestLimiterTest.java b/sentinel-cluster/sentinel-cluster-server-default/src/test/java/com/alibaba/csp/sentinel/cluster/flow/statistic/limit/GlobalRequestLimiterTest.java
new file mode 100644
index 0000000000..e618d7dec5
--- /dev/null
+++ b/sentinel-cluster/sentinel-cluster-server-default/src/test/java/com/alibaba/csp/sentinel/cluster/flow/statistic/limit/GlobalRequestLimiterTest.java
@@ -0,0 +1,56 @@
+/*
+ * Copyright 1999-2018 Alibaba Group Holding Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.alibaba.csp.sentinel.cluster.flow.statistic.limit;
+
+import com.alibaba.csp.sentinel.cluster.server.config.ClusterServerConfigManager;
+import com.alibaba.csp.sentinel.cluster.test.AbstractTimeBasedTest;
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Test;
+
+public class GlobalRequestLimiterTest extends AbstractTimeBasedTest {
+    @Before
+    public void preTest() {
+        ClusterServerConfigManager.setMaxAllowedQps(3);
+    }
+
+    @Test
+    public void testPass() throws InterruptedException {
+        setCurrentMillis(System.currentTimeMillis());
+        GlobalRequestLimiter.initIfAbsent("user");
+        Assert.assertNotNull(GlobalRequestLimiter.getRequestLimiter("user"));
+        Assert.assertEquals(3, GlobalRequestLimiter.getMaxAllowedQps("user"), 0.01);
+        Assert.assertTrue(GlobalRequestLimiter.tryPass("user"));
+        Assert.assertTrue(GlobalRequestLimiter.tryPass("user"));
+        Assert.assertTrue(GlobalRequestLimiter.tryPass("user"));
+        Assert.assertFalse(GlobalRequestLimiter.tryPass("user"));
+        Assert.assertEquals(3, GlobalRequestLimiter.getCurrentQps("user"), 0.01);
+
+        // wait a second to refresh the window
+        sleep(1000);
+        Assert.assertTrue(GlobalRequestLimiter.tryPass("user"));
+        Assert.assertTrue(GlobalRequestLimiter.tryPass("user"));
+        Assert.assertEquals(2, GlobalRequestLimiter.getCurrentQps("user"), 0.01);
+    }
+
+    @Test
+    public void testChangeMaxAllowedQps() {
+        GlobalRequestLimiter.initIfAbsent("foo");
+        Assert.assertEquals(3, GlobalRequestLimiter.getMaxAllowedQps("foo"), 0.01);
+        GlobalRequestLimiter.applyMaxQpsChange(10);
+        Assert.assertEquals(10, GlobalRequestLimiter.getMaxAllowedQps("foo"), 0.01);
+    }
+}
diff --git a/sentinel-cluster/sentinel-cluster-server-default/src/test/java/com/alibaba/csp/sentinel/cluster/flow/statistic/limit/RequestLimiterTest.java b/sentinel-cluster/sentinel-cluster-server-default/src/test/java/com/alibaba/csp/sentinel/cluster/flow/statistic/limit/RequestLimiterTest.java
new file mode 100644
index 0000000000..0d3f95e6af
--- /dev/null
+++ b/sentinel-cluster/sentinel-cluster-server-default/src/test/java/com/alibaba/csp/sentinel/cluster/flow/statistic/limit/RequestLimiterTest.java
@@ -0,0 +1,44 @@
+/*
+ * Copyright 1999-2018 Alibaba Group Holding Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.alibaba.csp.sentinel.cluster.flow.statistic.limit;
+
+import com.alibaba.csp.sentinel.cluster.test.AbstractTimeBasedTest;
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class RequestLimiterTest extends AbstractTimeBasedTest {
+
+    @Test
+    public void testRequestLimiter() {
+        setCurrentMillis(System.currentTimeMillis());
+        RequestLimiter limiter = new RequestLimiter(10);
+        limiter.add(3);
+        limiter.add(3);
+        limiter.add(3);
+        assertTrue(limiter.canPass());
+        assertEquals(9, limiter.getSum());
+        limiter.add(3);
+        assertFalse(limiter.canPass());
+
+        // wait a second to refresh the window
+        sleep(1000);
+        limiter.add(3);
+        assertTrue(limiter.tryPass());
+        assertTrue(limiter.canPass());
+        assertEquals(4, limiter.getSum());
+    }
+}
diff --git a/sentinel-cluster/sentinel-cluster-server-default/src/test/java/com/alibaba/csp/sentinel/cluster/flow/statistic/metric/ClusterMetricTest.java b/sentinel-cluster/sentinel-cluster-server-default/src/test/java/com/alibaba/csp/sentinel/cluster/flow/statistic/metric/ClusterMetricTest.java
new file mode 100644
index 0000000000..e8c286bc7c
--- /dev/null
+++ b/sentinel-cluster/sentinel-cluster-server-default/src/test/java/com/alibaba/csp/sentinel/cluster/flow/statistic/metric/ClusterMetricTest.java
@@ -0,0 +1,46 @@
+/*
+ * Copyright 1999-2018 Alibaba Group Holding Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.alibaba.csp.sentinel.cluster.flow.statistic.metric;
+
+import com.alibaba.csp.sentinel.cluster.flow.statistic.data.ClusterFlowEvent;
+import com.alibaba.csp.sentinel.cluster.test.AbstractTimeBasedTest;
+import org.junit.Assert;
+import org.junit.Test;
+
+public class ClusterMetricTest extends AbstractTimeBasedTest {
+
+    @Test
+    public void testTryOccupyNext() {
+        setCurrentMillis(System.currentTimeMillis());
+        ClusterMetric metric = new ClusterMetric(5, 25);
+        metric.add(ClusterFlowEvent.PASS, 1);
+        metric.add(ClusterFlowEvent.PASS, 2);
+        metric.add(ClusterFlowEvent.PASS, 1);
+        metric.add(ClusterFlowEvent.BLOCK, 1);
+        Assert.assertEquals(4, metric.getSum(ClusterFlowEvent.PASS));
+        Assert.assertEquals(1, metric.getSum(ClusterFlowEvent.BLOCK));
+        Assert.assertEquals(160, metric.getAvg(ClusterFlowEvent.PASS), 0.01);
+        Assert.assertEquals(200, metric.tryOccupyNext(ClusterFlowEvent.PASS, 111, 900));
+        metric.add(ClusterFlowEvent.PASS, 1);
+        metric.add(ClusterFlowEvent.PASS, 2);
+        metric.add(ClusterFlowEvent.PASS, 1);
+        Assert.assertEquals(200, metric.tryOccupyNext(ClusterFlowEvent.PASS, 222, 900));
+        metric.add(ClusterFlowEvent.PASS, 1);
+        metric.add(ClusterFlowEvent.PASS, 2);
+        metric.add(ClusterFlowEvent.PASS, 1);
+        Assert.assertEquals(0, metric.tryOccupyNext(ClusterFlowEvent.PASS, 333, 900));
+    }
+}
diff --git a/sentinel-cluster/sentinel-cluster-server-default/src/test/java/com/alibaba/csp/sentinel/cluster/flow/statistic/metric/ClusterParamMetricTest.java b/sentinel-cluster/sentinel-cluster-server-default/src/test/java/com/alibaba/csp/sentinel/cluster/flow/statistic/metric/ClusterParamMetricTest.java
new file mode 100644
index 0000000000..82645877ad
--- /dev/null
+++ b/sentinel-cluster/sentinel-cluster-server-default/src/test/java/com/alibaba/csp/sentinel/cluster/flow/statistic/metric/ClusterParamMetricTest.java
@@ -0,0 +1,56 @@
+/*
+ * Copyright 1999-2018 Alibaba Group Holding Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.alibaba.csp.sentinel.cluster.flow.statistic.metric;
+
+import com.alibaba.csp.sentinel.cluster.test.AbstractTimeBasedTest;
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class ClusterParamMetricTest extends AbstractTimeBasedTest {
+
+    @Test
+    public void testClusterParamMetric() {
+        setCurrentMillis(System.currentTimeMillis());
+        Map<Object, Double> topMap = new HashMap<Object, Double>();
+        ClusterParamMetric metric = new ClusterParamMetric(5, 25, 100);
+        metric.addValue("e1", -1);
+        metric.addValue("e1", -2);
+        metric.addValue("e2", 100);
+        metric.addValue("e2", 23);
+        metric.addValue("e3", 100);
+        metric.addValue("e3", 230);
+        Assert.assertEquals(-3, metric.getSum("e1"));
+        Assert.assertEquals(-120, metric.getAvg("e1"), 0.01);
+        topMap.put("e3", (double) 13200);
+        Assert.assertEquals(topMap, metric.getTopValues(1));
+        topMap.put("e2", (double) 4920);
+        topMap.put("e1", (double) -120);
+        Assert.assertEquals(topMap, metric.getTopValues(5));
+        metric.addValue("e2", 100);
+        metric.addValue("e2", 23);
+        Assert.assertEquals(246, metric.getSum("e2"));
+        Assert.assertEquals(9840, metric.getAvg("e2"), 0.01);
+    }
+
+    @Test(expected = IllegalArgumentException.class)
+    public void testIllegalArgument() {
+        ClusterParamMetric metric = new ClusterParamMetric(5, 25, 100);
+        metric.getTopValues(-1);
+    }
+}
diff --git a/sentinel-cluster/sentinel-cluster-server-default/src/test/java/com/alibaba/csp/sentinel/cluster/test/AbstractTimeBasedTest.java b/sentinel-cluster/sentinel-cluster-server-default/src/test/java/com/alibaba/csp/sentinel/cluster/test/AbstractTimeBasedTest.java
new file mode 100644
index 0000000000..d4458a0d21
--- /dev/null
+++ b/sentinel-cluster/sentinel-cluster-server-default/src/test/java/com/alibaba/csp/sentinel/cluster/test/AbstractTimeBasedTest.java
@@ -0,0 +1,55 @@
+/*
+ * Copyright 1999-2018 Alibaba Group Holding Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.alibaba.csp.sentinel.cluster.test;
+
+import com.alibaba.csp.sentinel.util.TimeUtil;
+import org.junit.runner.RunWith;
+import org.powermock.api.mockito.PowerMockito;
+import org.powermock.core.classloader.annotations.PrepareForTest;
+import org.powermock.modules.junit4.PowerMockRunner;
+
+/**
+ * Mock support for {@link TimeUtil}.
+ */
+@RunWith(PowerMockRunner.class)
+@PrepareForTest({TimeUtil.class})
+public abstract class AbstractTimeBasedTest {
+
+    private long currentMillis = 0;
+
+    {
+        PowerMockito.mockStatic(TimeUtil.class);
+        PowerMockito.when(TimeUtil.currentTimeMillis()).thenReturn(currentMillis);
+    }
+
+    protected final void useActualTime() {
+        PowerMockito.when(TimeUtil.currentTimeMillis()).thenCallRealMethod();
+    }
+
+    protected final void setCurrentMillis(long cur) {
+        currentMillis = cur;
+        PowerMockito.when(TimeUtil.currentTimeMillis()).thenReturn(currentMillis);
+    }
+
+    protected final void sleep(int t) {
+        currentMillis += t;
+        PowerMockito.when(TimeUtil.currentTimeMillis()).thenReturn(currentMillis);
+    }
+
+    protected final void sleepSecond(int timeSec) {
+        sleep(timeSec * 1000);
+    }
+}