alter: add a test case for simultaneous truncates

Tarantool should not crash if one space was truncated simultaneosly from
two fibers.

Closes #928

test/box/ddl.result

@@ -49,3 +49,40 @@ _ = box.space.test:drop()
 ---
 ...
 test_run:cmd('restart server default')
+env = require('test_run')
+---
+...
+test_run = env.new()
+---
+...
+fiber = require'fiber'
+---
+...
+ch = fiber.channel(2)
+---
+...
+--issue #928
+space = box.schema.space.create('test_trunc')
+---
+...
+_ = space:create_index('pk')
+---
+...
+_ = box.space.test_trunc:create_index('i1', {type = 'hash', parts = {2, 'STR'}})
+---
+...
+_ = box.space.test_trunc:create_index('i2', {type = 'hash', parts = {2, 'STR'}})
+---
+...
+function test_trunc() space:truncate() ch:put(true) end
+---
+...
+_ = {fiber.create(test_trunc), fiber.create(test_trunc)}
+---
+...
+_ = {ch:get(), ch:get()}
+---
+...
+space:drop()
+---
+...

test/box/ddl.test.lua

@@ -31,3 +31,20 @@ _ = box.space.test:drop()
 
 test_run:cmd('restart server default')
 
+env = require('test_run')
+test_run = env.new()
+fiber = require'fiber'
+
+ch = fiber.channel(2)
+
+--issue #928
+space = box.schema.space.create('test_trunc')
+_ = space:create_index('pk')
+_ = box.space.test_trunc:create_index('i1', {type = 'hash', parts = {2, 'STR'}})
+_ = box.space.test_trunc:create_index('i2', {type = 'hash', parts = {2, 'STR'}})
+
+function test_trunc() space:truncate() ch:put(true) end
+
+_ = {fiber.create(test_trunc), fiber.create(test_trunc)}
+_ = {ch:get(), ch:get()}
+space:drop()