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?

Answer 1

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

Answer 2

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