RSpec: Expecting method to raise an error fails

Question

I'm trying to test that an error is raised correctly under certain conditions. In this spec, the error is raised, but the test still fails. What am I doing wrong?

require 'spec_helper'

describe USBTeensyRenderer do 
  context 'when the correct USB port name is not present' do
    it 'raises an error on instantiation' do
      expect(renderer = USBTeensyRenderer.new).to raise_error(USBInitError)
    end
  end
end

And the terminal output of 'bundle exec rspec':

Failures:

  1) USBTeensyRenderer when the correct USB port name is not present raises an error on instantiation
     Failure/Error: expect(renderer = USBTeensyRenderer.new).to raise_error(USBInitError)
     USBInitError:
       USB output couldn't be initialized
     # ./lib/ivan/view/renderers/usb_teensy_renderer.rb:9:in `rescue in initialize'
     # ./lib/ivan/view/renderers/usb_teensy_renderer.rb:6:in `initialize'
     # ./spec/models/usb_teensy_renderer_spec.rb:10:in `new'
     # ./spec/models/usb_teensy_renderer_spec.rb:10:in `block (3 levels) in <top (required)>'

Finished in 0.00351 seconds (files took 0.11638 seconds to load)
8 examples, 1 failure

Failed examples:

rspec ./spec/models/usb_teensy_renderer_spec.rb:9 # USBTeensyRenderer when the correct USB port name is not present raises an error on instantiation

Here's how the error is raised in the class:

def initialize
  begin
    @sp = SerialPort.new("/dev/tty.usbmodem54121", 9600, 8, 1)
  rescue
    raise USBInitError, "USB output couldn't be initialized"
  end
  @sp.get_modem_params()
end

Answer 1

I believe expect should take a block in this case:

expect { renderer = USBTeensyRenderer.new }.to raise_error(USBInitError)

This thread has a pretty good explanation on expect() vs expect {}

Rspec: expect vs expect with block - what's the difference?