RSpec doesn't give me any backtrace

Hey,

I trying to get a backtrace with rspec but I can't get it working for
some reason.

This is the test file:
require 'spec_helper'

describe ActivityReport do
  it "should create a new instance given valid attributes" do
    activity = Factory(:activity_report)
  end
end

This is the command I run:
rspec --backtrace spec/models/activity_report_spec.rb

And this is what I get:
No examples matched {:focus=>true}. Running all.

ActivityReport
  should create a new instance given valid attributes (FAILED - 1)

Failures:

  1) ActivityReport should create a new instance given valid attributes
     Failure/Error: Unable to find matching line from backtrace
     SystemStackError:
       stack level too deep