RSpec: Testing with Threads

Question

In RSpec, I have function that creates a new thread, and inside that thread performs some action–in my case, calls TCPSocket#readline. Here's the function as it is right now:

def read
  Thread.new do
    while line = @socket.readline
      #TODO: stuff
    end
  end
end

Due to thread scheduling, my test will fail if written as such:

it "reads from socket" do
  subject.socket.should_receive(:readline)
  subject.read
end

Currently the only way I know to hack around this is to use sleep 0.1. Is there a way to properly delay the test until that thread is running?

Winfield · Accepted Answer · 2013-01-30 18:04:48Z

13

If your goal is to assert the system state is changed by the execution of your second thread, you should join on the second thread in your main test thread:

it "reads from socket" do
  subject.socket.should_receive(:readline)
  socket_thread = subject.read
  socket_thread.join
end

answered Jan 30, 2013 at 18:04

Winfield

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2 Comments

Nick Acker Over a year ago

Good call, in my n00bishness I completely forgot about the fact that it was returning the thread, so I didn't think to use it that way.

David Over a year ago

And what if the goal is not to wait on the thread to complete? Sort of like this: ruby-forum.com/topic/2477428 or alternate post code.activestate.com/lists/ruby-talk/20264

Trevor Turk · Accepted Answer · 2016-09-03 00:01:28Z

6

This is a bit of a hack, but here's a before block you can use in case you'd like the thread to yield but be able to call join at the end of the thread.

before do
  allow(Thread).to receive(:new).and_yield.and_return(Class.new { def join; end }.new)
end

answered Sep 3, 2016 at 0:01

Trevor Turk

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