# Testing - Network Layer Fault Injection in Ruby

**URL:** <https://www.ruby-forum.com/t/testing-network-layer-fault-injection-in-ruby/117218>\
**Category:** Ruby\
**Created:** [October 14, 2007, 10:24pm UTC](https://www.ruby-forum.com/t/testing-network-layer-fault-injection-in-ruby/117218 "2007-10-14T22:24:18Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![axees335](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/e68b1a/32.png) [@axees335](https://www.ruby-forum.com/u/axees335)\
**Post date:** [October 14, 2007, 10:24pm UTC](https://www.ruby-forum.com/t/testing-network-layer-fault-injection-in-ruby/117218/1 "2007-10-14T22:24:18Z")

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Hi all,

I’ve yet to find something that fills this hole in my test cases.

Does anyone do this, and if so, what tools do they use?

Thanks,

James.

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<div class="post-metadata">

**Author:** ![axees335](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/e68b1a/32.png) [@axees335](https://www.ruby-forum.com/u/axees335)\
**Post date:** [October 14, 2007, 10:59pm UTC](https://www.ruby-forum.com/t/testing-network-layer-fault-injection-in-ruby/117218/2 "2007-10-14T22:59:24Z")

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On Oct 14, 2007, at 13:23 , James T. wrote:

> I’ve yet to find something that fills this hole in my test cases.  
> Does anyone do this, and if so, what tools do they use?

I do some of this with custom stubs in memcache-client, see below.  
I’ve also simulated call failures (Errno::whatever) with slightly  
more powerful stubs that can take a block to raise the exception.

Here’s a fake socket:

class FakeSocket

attr\_reader :written, :data

def initialize  
@written = StringIO.new  
@data = StringIO.new  
end

def write(data)  
@written.write data  
end

def gets  
@data.gets  
end

def read(arg)  
@data.read arg  
end

end

And here’s a test using it:

def test\_flush\_all\_failure  
socket = FakeSocket.new  
socket.data.write “ERROR\r\n”  
socket.data.rewind  
server = FakeServer.new socket  
def server.host() “localhost”; end  
def server.port() 11211; end

```
 @cache.servers = []
 @cache.servers << server

 assert_raise MemCache::MemCacheError do
   @cache.flush_all
 end

 assert_equal "flush_all\r\n", socket.written.string

```

end

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<div class="post-metadata">

**Author:** ![axees335](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/e68b1a/32.png) [@axees335](https://www.ruby-forum.com/u/axees335)\
**Post date:** [October 14, 2007, 11:53pm UTC](https://www.ruby-forum.com/t/testing-network-layer-fault-injection-in-ruby/117218/3 "2007-10-14T23:53:48Z")

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Eric,

Thanks, that’s somewhat the route I had started down for some of the  
units. I probably shouldn’t have omitted from my orignal question, the  
fact that I’m also using OpenSSL.

Some of the specific issues I have been dealing with are caused by a  
harsh environment (trans-atlantic links and poor ADSL connections), and  
in some cases this causes irrecoverable blocking. I think I’ve managed  
to cover all of the blocking cases, but local tests are hard to  
implement, as you have to fake things like a full TCP connection  
timeout. (Which requires not sending and timing out packet data which  
normally the OS doesn’t want you to do).

It’s also difficult to find out where the blocks are, as the state  
renders the app essentially useless, and happens in a different  
environment than that of the testing / development stage.

As some of this connection state stuff is actually outside of pure ruby,  
I was somewhat hoping for an external solution, such as a fault  
injection proxy socket or similar. Do you know of any?

Regards,

James.

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<div class="post-metadata">

**Author:** ![axees335](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/e68b1a/32.png) [@axees335](https://www.ruby-forum.com/u/axees335)\
**Post date:** [October 15, 2007, 2:28am UTC](https://www.ruby-forum.com/t/testing-network-layer-fault-injection-in-ruby/117218/4 "2007-10-15T02:28:02Z")

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On Oct 14, 2007, at 14:52 , James T. wrote:

> packet data which normally the OS doesn’t want you to do).
> 
> It’s also difficult to find out where the blocks are, as the state  
> renders the app essentially useless, and happens in a different  
> environment than that of the testing / development stage.
> 
> As some of this connection state stuff is actually outside of pure  
> ruby, I was somewhat hoping for an external solution, such as a  
> fault injection proxy socket or similar. Do you know of any?

I don’t I’ve not needed that level of fault tolerance.