On Tue, Mar 10, 2015 at 7:50 PM, Jon Rowe <[email protected]> wrote:
The `change` matcher requires a block to execute so it can evaluate before
> / after, but the one liner syntax doesn’t support that, so you need to use
> the third form, to improve readability here you could use the named
> subject, `subject(:index) { get :index }` and thus `expect { index }.to
> change { assigns(:assets) }.from(nil)`
>
> Jon Rowe
> ---------------------------
> [email protected]
> jonrowe.co.uk
>
Technically, the one liner syntax does support blocks, but you have to make
your subject return a proc or lambda:
describe "GET #index" do
subject { lambda { get :index } }
# either of these work
it { is_expected.to change { assigns(:assets) }.from(nil) }
it { should change { assigns(:assets) }.from(nil) }end
I don’t think that’s a good use of RSpec’s API, though; the one-liner
syntax has valid uses but I don’t think this is a good case for it.
Actually, in this case I’m not even sure you need to use the change
matcher; aren’t all assigns initially nil before the controller action has
been called? (It’s been a long time since I’ve done any Rails but that’s
what I remember). If so, the change matcher seems unnecessary here; you
could just use a simpler specify { expect(assigns(:assets)).not_to be_nil }.
More generally, the reason the change matcher requires a block, proc or
lambda is because it observes a *side effect* (e.g. the mutation of some
state) rather than being a simple matcher applied to a value. The other
block matchers (raise_error, throw_symbol, yield_args, etc) similarly are
expectations about a side effect from running a bit of code rather than
being about the return value of an expression.
HTH,
Myron
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