From d4e2ab21fb3ea9c5003e051c092aa0df0e451883 Mon Sep 17 00:00:00 2001
From: Matthias Radestock <matthias@rabbitmq.com>
Date: Tue, 20 Nov 2012 17:51:33 +0000
Subject: some quick check tests all work ok, but then again that's also the
 case when I completely break vq.

---
 src/rabbit_backing_queue_qc.erl | 70 ++++++++++++++++++++++++++++-------------
 1 file changed, 48 insertions(+), 22 deletions(-)

diff --git a/src/rabbit_backing_queue_qc.erl b/src/rabbit_backing_queue_qc.erl
index b37fbb29..df242062 100644
--- a/src/rabbit_backing_queue_qc.erl
+++ b/src/rabbit_backing_queue_qc.erl
@@ -85,17 +85,19 @@ backing_queue_test(Cmds) ->
 
 %% Commands
 
-%% Command frequencies are tuned so that queues are normally reasonably
-%% short, but they may sometimes exceed ?QUEUE_MAXLEN. Publish-multiple
-%% and purging cause extreme queue lengths, so these have lower probabilities.
-%% Fetches are sufficiently frequent so that commands that need acktags
-%% get decent coverage.
+%% Command frequencies are tuned so that queues are normally
+%% reasonably short, but they may sometimes exceed
+%% ?QUEUE_MAXLEN. Publish-multiple and purging cause extreme queue
+%% lengths, so these have lower probabilities.  Fetches/drops are
+%% sufficiently frequent so that commands that need acktags get decent
+%% coverage.
 
 command(S) ->
     frequency([{10, qc_publish(S)},
                {1,  qc_publish_delivered(S)},
                {1,  qc_publish_multiple(S)},  %% very slow
-               {15, qc_fetch(S)},             %% needed for ack and requeue
+               {9,  qc_fetch(S)},             %% needed for ack and requeue
+               {6,  qc_drop(S)},              %%
                {15, qc_ack(S)},
                {15, qc_requeue(S)},
                {3,  qc_set_ram_duration_target(S)},
@@ -124,6 +126,9 @@ qc_publish_delivered(#state{bqstate = BQ}) ->
 qc_fetch(#state{bqstate = BQ}) ->
     {call, ?BQMOD, fetch, [boolean(), BQ]}.
 
+qc_drop(#state{bqstate = BQ}) ->
+    {call, ?BQMOD, drop, [boolean(), BQ]}.
+
 qc_ack(#state{bqstate = BQ, acks = Acks}) ->
     {call, ?BQMOD, ack, [rand_choice(proplists:get_keys(Acks)), BQ]}.
 
@@ -217,22 +222,10 @@ next_state(S, Res,
            };
 
 next_state(S, Res, {call, ?BQMOD, fetch, [AckReq, _BQ]}) ->
-    #state{len = Len, messages = Messages, acks = Acks} = S,
-    ResultInfo = {call, erlang, element, [1, Res]},
-    BQ1        = {call, erlang, element, [2, Res]},
-    AckTag     = {call, erlang, element, [3, ResultInfo]},
-    S1         = S#state{bqstate = BQ1},
-    case gb_trees:is_empty(Messages) of
-        true  -> S1;
-        false -> {SeqId, MsgProp_Msg, M2} = gb_trees:take_smallest(Messages),
-                 S2 = S1#state{len = Len - 1, messages = M2},
-                 case AckReq of
-                     true  ->
-                         S2#state{acks = [{AckTag, {SeqId, MsgProp_Msg}}|Acks]};
-                     false ->
-                         S2
-                 end
-    end;
+    next_state_fetch_and_drop(S, Res, AckReq, 3);
+
+next_state(S, Res, {call, ?BQMOD, drop, [AckReq, _BQ]}) ->
+    next_state_fetch_and_drop(S, Res, AckReq, 2);
 
 next_state(S, Res, {call, ?BQMOD, ack, [AcksArg, _BQ]}) ->
     #state{acks = AcksState} = S,
@@ -295,6 +288,21 @@ postcondition(S, {call, ?BQMOD, fetch, _Args}, Res) ->
             Len =:= 0
     end;
 
+postcondition(S, {call, ?BQMOD, drop, _Args}, Res) ->
+    #state{messages = Messages, len = Len, acks = Acks, confirms = Confrms} = S,
+    case Res of
+        {{MsgIdFetched, AckTag, RemainingLen}, _BQ} ->
+            {_SeqId, {_MsgProps, Msg}} = gb_trees:smallest(Messages),
+            MsgId = {call, erlang, element,
+                     [?RECORD_INDEX(id, basic_message), Msg]},
+            MsgIdFetched =:= MsgId andalso
+            not proplists:is_defined(AckTag, Acks) andalso
+                not gb_sets:is_element(AckTag, Confrms) andalso
+                RemainingLen =:= Len - 1;
+        {empty, _BQ} ->
+            Len =:= 0
+    end;
+
 postcondition(S, {call, ?BQMOD, publish_delivered, _Args}, {AckTag, _BQ}) ->
     #state{acks = Acks, confirms = Confrms} = S,
     not proplists:is_defined(AckTag, Acks) andalso
@@ -388,6 +396,24 @@ drop_messages(Messages) ->
             end
     end.
 
+next_state_fetch_and_drop(S, Res, AckReq, AckTagIdx) ->
+    #state{len = Len, messages = Messages, acks = Acks} = S,
+    ResultInfo = {call, erlang, element, [1, Res]},
+    BQ1        = {call, erlang, element, [2, Res]},
+    AckTag     = {call, erlang, element, [AckTagIdx, ResultInfo]},
+    S1         = S#state{bqstate = BQ1},
+    case gb_trees:is_empty(Messages) of
+        true  -> S1;
+        false -> {SeqId, MsgProp_Msg, M2} = gb_trees:take_smallest(Messages),
+                 S2 = S1#state{len = Len - 1, messages = M2},
+                 case AckReq of
+                     true  ->
+                         S2#state{acks = [{AckTag, {SeqId, MsgProp_Msg}}|Acks]};
+                     false ->
+                         S2
+                 end
+    end.
+
 -else.
 
 -export([prop_disabled/0]).
-- 
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