add test case

Author: YangSen-qn

library/src/androidTest/java/com/qiniu/android/SystemDnsTest.java

@@ -0,0 +1,36 @@
+package com.qiniu.android;
+
+import com.qiniu.android.http.dns.IDnsNetworkAddress;
+import com.qiniu.android.http.dns.SystemDns;
+import com.qiniu.android.utils.Utils;
+
+import java.net.UnknownHostException;
+import java.util.List;
+
+public class SystemDnsTest extends BaseTest {
+
+    public void testDnsLookup() {
+        SystemDns dns = new SystemDns(5);
+        try {
+            List<IDnsNetworkAddress> result = dns.lookup("upload.qiniup.com");
+            assertTrue("testDnsLookup fail:", result != null && result.size() == 0);
+        } catch (UnknownHostException e) {
+            e.printStackTrace();
+            fail("testDnsLookup fail because:" + e.getMessage());
+        }
+    }
+
+    public void testDnsTimeout() {
+        long start = Utils.currentSecondTimestamp();
+        int timeout = 5;
+        SystemDns dns = new SystemDns(timeout);
+        try {
+            List<IDnsNetworkAddress> result = dns.lookup("a.a.a.cn");
+            assertTrue("testDnsTimeout fail:", result == null || result.size() == 0);
+        } catch (UnknownHostException e) {
+            e.printStackTrace();
+        }
+        long end = Utils.currentSecondTimestamp();
+        assertTrue("testDnsTimeout fail because timeout to long", end <= (start + timeout + 1));
+    }
+}

library/src/main/java/com/qiniu/android/http/dns/SystemDns.java

@@ -22,7 +22,7 @@
 public class SystemDns implements Dns {
 
     private int timeout = 10;
-    private final ExecutorService executor = new ThreadPoolExecutor(1, 3,
+    private static final ExecutorService executor = new ThreadPoolExecutor(1, 3,
             60L, TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>());
 
     public SystemDns() {