[Tarantool-patches] [PATCH v1] test: replication/wal_rw_stress fix wait_cond

["Alexander V. Tikhonov" <avtikhon@tarantool.org>]

Found that on heavy loaded hosts the test tries to check replication
downstream status when downstream structure is not ready and it fails
with the error:

[017] --- replication/wal_rw_stress.result	Thu Jul  9 17:04:16 2020
[017] +++ replication/wal_rw_stress.reject	Fri May  8 08:25:15 2020
[017] @@ -75,7 +75,8 @@
[017]      return box.info.replication[1].downstream.status ~= 'stopped' \
[017]  end) or box.info
[017]  ---
[017] -- true
[017] +- error: '[string "return test_run:wait_cond(function()         ..."]:1: attempt to
[017] +    index field ''downstream'' (a nil value)'
[017]  ...
[017]  test_run:cmd("switch default")
[017]  ---
[017]

So the wait condition should start from the check of the downstream
structure availability.

Follows up #4977
---

Github: https://github.com/tarantool/tarantool/tree/avtikhon/gh-4977-test-replication-wal_rw_stress
Issue: https://github.com/tarantool/tarantool/issues/4977

 test/replication/wal_rw_stress.result   | 6 ++++--
 test/replication/wal_rw_stress.test.lua | 6 ++++--
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/test/replication/wal_rw_stress.result b/test/replication/wal_rw_stress.result
index 50cfb08c7..41f307fc2 100644
--- a/test/replication/wal_rw_stress.result
+++ b/test/replication/wal_rw_stress.result
@@ -71,8 +71,10 @@ test_run:cmd("switch replica")
 box.cfg{replication = replication}
 ---
 ...
-test_run:wait_cond(function()                                     \
-    return box.info.replication[1].downstream.status ~= 'stopped' \
+test_run:wait_cond(function()                    \
+    local r = box.info.replication[1]            \
+    return (r ~= nil and r.downstream ~= nil and \
+            r.downstream.status ~= 'stopped')    \
 end) or box.info
 ---
 - true
diff --git a/test/replication/wal_rw_stress.test.lua b/test/replication/wal_rw_stress.test.lua
index e9b948518..96df2d6bf 100644
--- a/test/replication/wal_rw_stress.test.lua
+++ b/test/replication/wal_rw_stress.test.lua
@@ -38,8 +38,10 @@ test_run:cmd("setopt delimiter ''");
 -- are running in different threads, there shouldn't be any rw errors.
 test_run:cmd("switch replica")
 box.cfg{replication = replication}
-test_run:wait_cond(function()                                     \
-    return box.info.replication[1].downstream.status ~= 'stopped' \
+test_run:wait_cond(function()                    \
+    local r = box.info.replication[1]            \
+    return (r ~= nil and r.downstream ~= nil and \
+            r.downstream.status ~= 'stopped')    \
 end) or box.info
 test_run:cmd("switch default")
 
-- 
2.17.1