I can sort-of see how to do this for Rect and Oval (as they have the same parameter inputs), but Arc has two additional parameters.

After playing around, I came up with something like this:

```ruby
shared_examples_for "left, top as center" do | *params |
  let(:centered_object) { described_class.new(app, 100, 50, 40, 20, *params, :center => true) }
  it "should now have a (left, top) origin" do
    centered_object.left.should eq(80)
    centered_object.top.should eq(40)
    centered_object.right.should eq(120)
    centered_object.bottom.should eq(60)
    centered_object.width.should eq(40)
    centered_object.height.should eq(20)
  end
end
```

Which gets the 'intended' effect, but may not be the best way to do it, i.e for Arc:

```ruby
it_behaves_like "left, top as center", 0, Shoes::TWO_PI
```

And Rect / Oval:

```ruby
it_behaves_like "left, top as center"
```

(thoughts?)