Make bgp_peer_test more stable

This test used to fail occasionally when the StateMachine tried to
delete the mock TcpSession which would have an invalid refcount 0.

Fix by using a mock StateMachine which overrides the DeleteSession
method.

Change-Id: Ibf2654477b4f6d995d8be757ac636dee4a4901b1
Partial-Bug: 1602347

src/bgp/state_machine.h

@@ -94,7 +94,7 @@ class StateMachine : public sc::state_machine<StateMachine, fsm::Idle> {
     };
 
     explicit StateMachine(BgpPeer *peer);
-    ~StateMachine();
+    virtual ~StateMachine();
 
     void Initialize();
     void Shutdown(int subcode);
@@ -125,7 +125,7 @@ class StateMachine : public sc::state_machine<StateMachine, fsm::Idle> {
     bool IdleHoldTimerRunning();
 
     void StartSession();
-    void DeleteSession(BgpSession *session);
+    virtual void DeleteSession(BgpSession *session);
     void AssignSession(bool active);
 
     virtual void OnSessionEvent(TcpSession *session, TcpSession::Event event);

src/bgp/test/bgp_peer_test.cc

@@ -7,6 +7,7 @@
 #include "base/task_annotations.h"
 #include "base/test/task_test_util.h"
 #include "bgp/bgp_config.h"
+#include "bgp/bgp_factory.h"
 #include "bgp/bgp_log.h"
 #include "bgp/bgp_peer.h"
 #include "bgp/bgp_session.h"
@@ -15,6 +16,12 @@
 // Use this test to mock BgpPeer and test selected functionality in BgpPeer as
 // desired. e.g. EndOfRibSendTimerExpired() API.
 
+class StateMachineMock : public StateMachine {
+public:
+    explicit StateMachineMock(BgpPeer *peer) : StateMachine(peer) { }
+    virtual void DeleteSession(BgpSession *session) { }
+};
+
 class BgpSessionMock : public BgpSession {
 public:
     BgpSessionMock(BgpSessionManager *manager)
@@ -415,6 +422,8 @@ INSTANTIATE_TEST_CASE_P(BgpPeerTestWithParams, BgpPeerParamTest,
 static void SetUp() {
     bgp_log_test::init();
     ControlNode::SetDefaultSchedulingPolicy();
+    BgpObjectFactory::Register<StateMachine>(
+        boost::factory<StateMachineMock *>());
 }
 
 static void TearDown() {