In a subject block, you can access the example (and it’s metadata) by
adding a block argument. So if you wanted to define a subject based on the
described_class and the group description, you could do:
subject { |ex| described_class.fields[ex.metadata[:example_group][:description]]
}
To take this a step further, you could define this in a shared context to
make it easy to apply this to multiple example groups:
RSpec.shared_context "dynamic field subject" do
subject { |ex|
described_class.fields[ex.metadata[:example_group][:description]] }
end
Then you can include this by using include_context:
RSpec.describe Types::Event do
describe "latitude" do
include_context "dynamic field subject"
# ...
endend
Taking this a step further, if you wanted to auto-include the shared
context, you can do so using config:
RSpec.configure do |config|
config.include_context "dynamic field subject",
:needs_dynamic_field_subjectend
Any group tagged with :needs_dynamic_field_subject will automatically have
this context included. You could even use define_derived_metadata to
automatically tag the desired groups with : needs_dynamic_field_subject:
RSpec.configure do |config|
config.define_derived_metadata do |meta|
meta[:needs_dynamic_field_subject] if satisfies_your_criteria?(meta)
endend
(The definition of satisfies_your_criteria? is left as an exercise to the
reader).
All that said: once you’ve done all that, things are wired up in a pretty
implicit manner, which can become quite confusing. The power is there in
RSpec to do this, but it doesn’t necessarily mean you should. Think
carefully about the tradeoffs involved and if it is the right solution for
your project.
My book Effective Testing with RSpec 3
<https://pragprog.com/book/rspec3/effective-testing-with-rspec-3> has a lot
more detail about this stuff if you want to know more.
HTH,
Myron
On Mon, Dec 4, 2017 at 8:10 AM, Steve V <[email protected]> wrote:
> how can I dynamically set the subject for a spec? I have a bunch of
> describe blocks that set the subject like this `subject {
> Types::Event.fields['latitude'] }`, where `Types::Event` is the
> `described_class`. The name of the describe block in this case is
> 'latitude'.
>
> Is there a way to get that name from the group, and set it on the subject,
> or maybe do something using a metadata flag?
>
> Thanks,
> Steve
>
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