diff --git a/src/dbms_simulator.cpp b/src/dbms_simulator.cpp
index f4b2565..06332c4 100644
--- a/src/dbms_simulator.cpp
+++ b/src/dbms_simulator.cpp
@@ -57,7 +57,7 @@ public:
     dbms_storage_engine()
         : mutex_()
         , transactions_()
-        , alg_freq_(100)
+        , alg_freq_(0)
         , bf_aborts_()
     { }
 
@@ -343,6 +343,7 @@ private:
     }
     int commit(trrep::transaction_context& transaction_context) override
     {
+        assert(mode() == trrep::client_context::m_applier);
         int ret(0);
         ret = transaction_context.before_commit();
         ret = ret || transaction_context.ordered_commit();
@@ -461,7 +462,7 @@ private:
 
     void report_progress(size_t i) const
     {
-        if ((i % 100) == 0)
+        if ((i % 1000) == 0)
         {
             trrep::log() << "client: " << id().get()
                          << " transactions: " << i
diff --git a/src/mock_provider.hpp b/src/mock_provider.hpp
index 80fe8c8..e35759e 100644
--- a/src/mock_provider.hpp
+++ b/src/mock_provider.hpp
@@ -105,14 +105,23 @@ namespace trrep
 
         int replay(wsrep_ws_handle_t*, void*) { ::abort(); /* not impl */}
 
+        int sst_sent(const wsrep_gtid_t&, int) { return 0; }
+        int sst_received(const wsrep_gtid_t&, int) { return 0; }
+
+        std::vector<status_variable> status() const
+        {
+            return std::vector<status_variable>();
+        }
+
+
         // Methods to modify mock state
 
-        // Inject BF abort event into the provider.
-        //
-        // @param bf_seqno Aborter sequence number
-        // @param trx_id Trx id to be aborted
-        // @param[out] victim_seqno
-        //
+        /*! Inject BF abort event into the provider.
+         *
+         * \param bf_seqno Aborter sequence number
+         * \param trx_id Trx id to be aborted
+         * \param[out] victim_seqno
+         */
         wsrep_status_t bf_abort(wsrep_seqno_t bf_seqno,
                                 wsrep_trx_id_t trx_id,
                                 wsrep_seqno_t* victim_seqno)
@@ -127,13 +136,11 @@ namespace trrep
             return WSREP_OK;
         }
 
-        int sst_sent(const wsrep_gtid_t&, int) { return 0; }
-        int sst_received(const wsrep_gtid_t&, int) { return 0; }
-
-        std::vector<status_variable> status() const
-        {
-            return std::vector<status_variable>();
-        }
+        /*!
+         * \todo Inject an error so that the next call to any
+         *       provider call will return the given error.
+         */
+        void inject_error(wsrep_status_t);
     private:
         wsrep_uuid_t group_id_;
         wsrep_uuid_t node_id_;
diff --git a/src/transaction_context.cpp b/src/transaction_context.cpp
index 76f234f..bc6bacc 100644
--- a/src/transaction_context.cpp
+++ b/src/transaction_context.cpp
@@ -189,6 +189,8 @@ int trrep::transaction_context::before_commit()
            state() == s_committing ||
            state() == s_must_abort ||
            state() == s_replaying);
+    assert((client_context_.mode() == trrep::client_context::m_replicating &&
+            state() == s_executing) || certified());
 
     switch (client_context_.mode())
     {