Bugzilla – Bug 15104
Nested async tests freeze Touch.Unit test runner
Last modified: 2014-09-04 08:17:27 EDT
I'm running into some cases where test cases that involve nested async calls
are resulting in the Touch.Unit runner freezing up. Here's a simple example of
a test that freezes it:
public async Task Repro()
await Task.Run(async() =>
When I run the app and hit Run Everything, it freezes up. Here is the log
2013-10-01 15:10:17.386 AsyncTestRepro[8915:1503] MonoTouch: Socket error while
connecting to MonoDevelop on 127.0.0.1:10000: Connection refused
2013-10-01 15:10:19.080 AsyncTestRepro[8915:a0b] [Runner executing: Run
2013-10-01 15:10:19.081 AsyncTestRepro[8915:a0b] [MonoTouch Version: 7.0.1]
2013-10-01 15:10:19.081 AsyncTestRepro[8915:a0b] [iPhone Simulator: iPhone
2013-10-01 15:10:19.082 AsyncTestRepro[8915:a0b] [Device Name: iPhone
2013-10-01 15:10:19.083 AsyncTestRepro[8915:a0b] [Device UDID:
2013-10-01 15:10:19.084 AsyncTestRepro[8915:a0b] [Device Locale: en_US]
2013-10-01 15:10:19.090 AsyncTestRepro[8915:a0b] [Device Date/Time:
10/1/2013 3:10:19 PM]
2013-10-01 15:10:19.091 AsyncTestRepro[8915:a0b] [Bundle:
2013-10-01 15:10:19.096 AsyncTestRepro[8915:a0b] AsyncTestRepro
2013-10-01 15:10:19.096 AsyncTestRepro[8915:a0b] ReproTests
Xamarin Studio 4.0.12
Xamarin.iOS 220.127.116.11 (Business Edition)
Mono 3.2.3 ((no/8d3b4b7)
The SynchronizationContext that is used with NUnitLite when doing async work
does not play well with the UIKitSynchronizationContext (i.e. you end up
waiting on the thread scheduled to do the work).
That's something I want to fix with the update to NUnitLite 1.0 - but that
won't be available in XI until it's done (and well tested). You might want to
track the githut repo until then (fix will be available there, to test, before
new XI versions).
Fixed in Touch.Unit / master 16062835e1e9ba01f4fb464f918db2e03c8ccb34
Like I said it might take a while (i.e. not the next maintenance release)
before this gets into XI. Look for release notes stating NUnitLite 1.0 support
You might have noticed that I had to revert my original fix - as it broke other
tests. I do have a workaround in mind.
Fixed in master 392c3611b11612894e9b4cfb5ed50b48e8de0cf9
Tests that cannot be executed from the main thread can use the [Timeout]
attribute (e.g. with Int32.MaxValue) to have the nunit framework run it into a
That keeps the default Touch.Unit runner behaviour of using the main (UI)
thread - and let you mark any test that you need to execute on a different
This fix is planned to be released with Xamarin.iOS 7.0.6, which should hit the
beta channel before December 23rd.
I have checked this issue with following steps and we are getting the same
1. Created iOS unit test project.
2. Added above test case into "Tests.cs" file.
3. Debug test on simulator.
4. run created test "repo" and observed that test get freeze
Refer screen shot :http://screencast.com/t/IR7d3RC9h
XS 4.2.3 (build 20)
X iOS 18.104.22.168
The fix is in Touch.Unit version 1.0. Xamarin.iOS ships 7.0.x ships version
0.9. Version 1.0 ships with XI 7.1.x (alpha). Changing milestone.
Also you did not follow the requirement stated in comment #4, which is adding a
[Timeout (Int32.MaxValue)] attribute to test requiring to be run on a
Does that mean that any async test would need to have that attribute then? That
is less than ideal, since that makes it different from other platforms that can
run the tests as-is. If that's the case, would it be possible to just imply
that attribute if a test is marked as async, or returns a Task?
I also realize this could just be an NUnitLite vs NUnit difference in general,
rather than a runner problem, so if that's the case I understand and the
attribute is easier to justify.
> any async test
No, just the ones that assume they run on a background thread. That's not very
common (e.g. one case in all the mono unit tests).
> that makes it different from other platforms
Not really. The attribute is part of the NUnit.Framework - and it's the only
one in NUnitLite that allows control on thread being used (more control exists
in the full NUnit framework).
OTOH adding the attribute makes your test more similar (not different) that
other platforms (see below for why) and it's precense won't really affect other
> would it be possible to just imply
> that attribute if a test is marked as async, or returns a Task?
Not without forking NUnitLite and make some rather big changes (it's not under
the runner control). That would make it hard to update to new versions and
likely cause other compatibility issues.
> rather than a runner problem
It's a runner difference. Most people does not realize it but many runners run
the tests in a background thread (by default). OTOH Touch.Unit does not because
a lot of iOS API requires to be executed from the main thread (and it's _much_
easier to get things into the background that getting them back on the main
Sorry for the misunderstanding, and thanks for the quick detailed response!
I'm still a little confused on the first part, about whether async tests need
that attribute now. Taking my original test case as an example, it just awaits
a delay. Originally this caused the UI thread to hang, so I'm guessing that
means it should get that attribute now? If that's the case, I'm not sure I
understand when there'd be an async test that didn't require it, since this is
a very simple example of async. Am I just missing something entirely here?
I have checked this issue, I added attributes "[Timeout (Int32.MaxValue)]" in
test method. Debug application on simulator and run all test successfully.
Screen cast: http://screencast.com/t/3Aka2Zgkb
XS 4.2.3 (build 51)
X iOS 22.214.171.124
Adding the Timeout attribute does not really help.
As you can see in the above screenshot (http://screencast.com/t/3Aka2Zgkb), yes
the Repo test reports successful but with 0 assertions - the assertions are