[PATCH] test: fix box/push.test sporadic hang

[Vladimir Davydov <vdavydov.dev@gmail.com>]

This patch fixes the following test failure:

 | --- box/push.result	Thu Jan 24 13:10:04 2019
 | +++ var/001_box/push.result	Thu Jan 24 13:13:08 2019
 | @@ -536,17 +536,3 @@
 |  ---
 |  ...
 |  chan_disconnected:get()
 | ----
 | -- true
 | -...
 | -chan_push:put(true)
 | ----
 | -- true
 | -...
 | -chan_push:get()
 | ----
 | -- Session is closed
 | -...
 | -box.schema.func.drop('do_long_and_push')
 | ----
 | -...

The problem occurs because the main fiber may close the connection
before do_long_and_push sets the session.on_disconnect trigger, in
which case chan_disconnected:get() will never return. Fix this by
setting the trigger in the main fiber and adding another channel
to wait for do_long_and_push function to start. Also, don't forget
to clear the trigger once the test is complete.

Fixes commit 43af2de2b129 ("session: outdate a session of a closed
connection").

Closes #3947
---
https://github.com/tarantool/tarantool/issues/3947
https://github.com/tarantool/tarantool/commits/dv/test-fixes

 test/box/push.result   | 15 ++++++++++++++-
 test/box/push.test.lua |  6 +++++-
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/test/box/push.result b/test/box/push.result
index 8919a3f5..aebcb750 100644
--- a/test/box/push.result
+++ b/test/box/push.result
@@ -501,18 +501,24 @@ s:drop()
 -- gh-3859: box.session.push() succeeds even after the connection
 -- is closed.
 --
+chan_func = fiber.channel()
+---
+...
 chan_push = fiber.channel()
 ---
 ...
 chan_disconnected = fiber.channel()
 ---
 ...
+on_disconnect = box.session.on_disconnect(function() chan_disconnected:put(true) end)
+---
+...
 test_run:cmd("setopt delimiter ';'")
 ---
 - true
 ...
 function do_long_and_push()
-    box.session.on_disconnect(function() chan_disconnected:put(true) end)
+    chan_func:put(true)
     chan_push:get()
     ok, err = box.session.push(100)
     chan_push:put(err)
@@ -532,6 +538,10 @@ box.schema.user.grant('guest', 'execute', 'function', 'do_long_and_push')
 f = fiber.create(function() c:call('do_long_and_push') end)
 ---
 ...
+chan_func:get()
+---
+- true
+...
 c:close()
 ---
 ...
@@ -550,3 +560,6 @@ chan_push:get()
 box.schema.func.drop('do_long_and_push')
 ---
 ...
+box.session.on_disconnect(nil, on_disconnect)
+---
+...
diff --git a/test/box/push.test.lua b/test/box/push.test.lua
index 514c08b3..7ae6f4a8 100644
--- a/test/box/push.test.lua
+++ b/test/box/push.test.lua
@@ -242,11 +242,13 @@ s:drop()
 -- gh-3859: box.session.push() succeeds even after the connection
 -- is closed.
 --
+chan_func = fiber.channel()
 chan_push = fiber.channel()
 chan_disconnected = fiber.channel()
+on_disconnect = box.session.on_disconnect(function() chan_disconnected:put(true) end)
 test_run:cmd("setopt delimiter ';'")
 function do_long_and_push()
-    box.session.on_disconnect(function() chan_disconnected:put(true) end)
+    chan_func:put(true)
     chan_push:get()
     ok, err = box.session.push(100)
     chan_push:put(err)
@@ -255,8 +257,10 @@ test_run:cmd("setopt delimiter ''");
 box.schema.func.create('do_long_and_push')
 box.schema.user.grant('guest', 'execute', 'function', 'do_long_and_push')
 f = fiber.create(function() c:call('do_long_and_push') end)
+chan_func:get()
 c:close()
 chan_disconnected:get()
 chan_push:put(true)
 chan_push:get()
 box.schema.func.drop('do_long_and_push')
+box.session.on_disconnect(nil, on_disconnect)
-- 
2.11.0