ZOOKEEPER-4270: Flaky test: QuorumPeerMainTest#testLeaderOutOfView

The test case is expecting node3 to be leader but node2 sometimes becomes leader. This happens because leader election completes between node1 and node2 which is valid.
Changed the expectations when node2 is leader otherwise kept the same expectations

Author: Mohammad Arshad <arshad@apache.org>

Reviewers: Enrico Olivelli <eolivelli@apache.org>

Closes #1666 from arshadmohammad/ZOOKEEPER-4270-master

zookeeper-server/src/test/java/org/apache/zookeeper/server/quorum/QuorumPeerMainTest.java

@@ -903,11 +903,26 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
                         "waiting for server to start");
             }
 
-            assertTrue(svrs.mt[0].getQuorumPeer().getPeerState() == QuorumPeer.ServerState.LOOKING);
-            assertTrue(svrs.mt[highestServerIndex].getQuorumPeer().getPeerState()
-                                      == QuorumPeer.ServerState.LEADING);
+            // Expecting that only 3 node will be leader is wrong, even 2 node can be leader, when cluster is formed with 1 node
+            boolean firstAndSecondNodeFormedCluster = false;
+            if (QuorumPeer.ServerState.LEADING == svrs.mt[1].getQuorumPeer().getPeerState()) {
+                assertEquals(QuorumPeer.ServerState.FOLLOWING,
+                    svrs.mt[0].getQuorumPeer().getPeerState());
+                assertEquals(QuorumPeer.ServerState.FOLLOWING,
+                    svrs.mt[highestServerIndex].getQuorumPeer().getPeerState());
+                firstAndSecondNodeFormedCluster = true;
+            } else {
+                // Verify leader out of view scenario
+                assertEquals(QuorumPeer.ServerState.LOOKING,
+                    svrs.mt[0].getQuorumPeer().getPeerState());
+                assertEquals(QuorumPeer.ServerState.LEADING,
+                    svrs.mt[highestServerIndex].getQuorumPeer().getPeerState());
+            }
             for (int i = 1; i < highestServerIndex; i++) {
-                assertTrue(svrs.mt[i].getQuorumPeer().getPeerState() == QuorumPeer.ServerState.FOLLOWING);
+                assertTrue(
+                    svrs.mt[i].getQuorumPeer().getPeerState() == QuorumPeer.ServerState.FOLLOWING
+                        || svrs.mt[i].getQuorumPeer().getPeerState()
+                        == QuorumPeer.ServerState.LEADING);
             }
 
             // Look through the logs for output that indicates Node 1 is LEADING or FOLLOWING
@@ -920,13 +935,18 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
                 foundLeading = leading.matcher(line).matches();
                 foundFollowing = following.matcher(line).matches();
             }
+            if (firstAndSecondNodeFormedCluster) {
+                assertTrue(foundFollowing,
+                    "Corrupt peer should join quorum with servers having same server configuration");
+            } else {
+                assertFalse(foundLeading, "Corrupt peer should never become leader");
+                assertFalse(foundFollowing,
+                    "Corrupt peer should not attempt connection to out of view leader");
+            }
 
         } finally {
             qlogger.removeAppender(appender);
         }
-
-        assertFalse(foundLeading, "Corrupt peer should never become leader");
-        assertFalse(foundFollowing, "Corrupt peer should not attempt connection to out of view leader");
     }
 
     @Test