refactor(pd): make the RaftEngine constructor private

hugegraph-pd/hg-pd-core/src/main/java/org/apache/hugegraph/pd/raft/RaftEngine.java

@@ -95,7 +95,7 @@ public class RaftEngine {
     private volatile int alivePeerCount = -1;
     private ScheduledExecutorService alivePeersRefresher;
 
-    public RaftEngine() {
+    private RaftEngine() {
         this.stateMachine = new RaftStateMachine();
     }
 

hugegraph-pd/hg-pd-test/src/main/java/org/apache/hugegraph/pd/core/store/RaftKVStoreTest.java

@@ -17,6 +17,7 @@
 
 package org.apache.hugegraph.pd.core.store;
 
+import java.lang.reflect.Constructor;
 import java.nio.ByteBuffer;
 import java.util.Collections;
 import java.util.List;
@@ -131,9 +132,9 @@ public void testWritesReachStoreOnlyThroughRaft() throws PDException {
     }
 
     @Test
-    public void testWriteOnNonLeaderIsRejectedAndNotApplied() throws PDException {
+    public void testWriteOnNonLeaderIsRejectedAndNotApplied() throws Exception {
         // A RaftEngine that has not joined a group is never leader
-        RaftKVStore notLeader = new RaftKVStore(new RaftEngine(), this.store);
+        RaftKVStore notLeader = new RaftKVStore(newEngine(), this.store);
 
         PDException e = Assert.assertThrows(PDException.class, () -> notLeader.put(KEY, VALUE));
 
@@ -236,4 +237,10 @@ private static void assertWriteFails(Write write) {
         Assert.assertTrue(e.getMessage(),
                           e.getMessage().contains("Error code = " + Pdpb.ErrorType.UNKNOWN_VALUE));
     }
+
+    private static RaftEngine newEngine() throws Exception {
+        Constructor<RaftEngine> constructor = RaftEngine.class.getDeclaredConstructor();
+        constructor.setAccessible(true);
+        return constructor.newInstance();
+    }
 }

hugegraph-pd/hg-pd-test/src/main/java/org/apache/hugegraph/pd/raft/RaftEngineReadinessTest.java

@@ -17,6 +17,7 @@
 
 package org.apache.hugegraph.pd.raft;
 
+import java.lang.reflect.Constructor;
 import java.util.Arrays;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.TimeUnit;
@@ -56,15 +57,21 @@ public class RaftEngineReadinessTest {
     private RaftStateMachine stateMachine;
 
     @Before
-    public void setUp() {
+    public void setUp() throws Exception {
         // Other suites leave scheduled tasks reading the shared engine. Keep this mock
         // private to the test so their isLeader() calls cannot affect interaction checks.
-        engine = new RaftEngine();
+        engine = newEngine();
         mockNode = mock(Node.class);
         stateMachine = Whitebox.getInternalState(engine, "stateMachine");
         Whitebox.setInternalState(engine, "raftNode", mockNode);
     }
 
+    private static RaftEngine newEngine() throws Exception {
+        Constructor<RaftEngine> constructor = RaftEngine.class.getDeclaredConstructor();
+        constructor.setAccessible(true);
+        return constructor.newInstance();
+    }
+
     private static LeaderChangeContext ctx() {
         return new LeaderChangeContext(LEADER, 5, Status.OK());
     }