Refactor notifiable_available? method

This method was calling `check_availability`, which returned a boolean
value and caused a `Naming/PredicateMethod` when upgrading rubocop.

So we're changing the logic a little bit to remove the
`check_availability` method and merge the tests of `check_availability`
and `notifiable_available?` (which were almost identical) together.

spec/models/proposal_notification_spec.rb

@@ -126,27 +126,21 @@ describe ProposalNotification do
 
         expect(notification.notifiable_available?).to be false
       end
-    end
-
-    describe "check_availability" do
-      it "returns true if the resource is present, not hidden, nor retired" do
-        notification = create(:notification, notifiable: notifiable)
-
-        expect(notification.check_availability(proposal)).to be true
-      end
 
       it "returns false if the resource is not present" do
         notification = create(:notification, notifiable: notifiable)
 
         notifiable.proposal.really_destroy!
-        expect(notification.check_availability(proposal)).to be false
+
+        expect(notification.notifiable_available?).to be false
       end
 
       it "returns false if the resource is hidden" do
         notification = create(:notification, notifiable: notifiable)
 
         notifiable.proposal.hide
-        expect(notification.check_availability(proposal)).to be false
+
+        expect(notification.notifiable_available?).to be false
       end
 
       it "returns false if the resource is retired" do
@@ -155,7 +149,8 @@ describe ProposalNotification do
         notifiable.proposal.update!(retired_at: Time.current,
                                     retired_explanation: "Unfeasible reason explanation",
                                     retired_reason: "unfeasible")
-        expect(notification.check_availability(proposal)).to be false
+
+        expect(notification.notifiable_available?).to be false
       end
     end
 

spec/shared/models/notifiable.rb

@@ -17,7 +17,7 @@ shared_examples "notifiable" do
   end
 
   describe "notifiable_available?" do
-    it "returns true when it's a root comment and the notifiable is available" do
+    it "returns true if the resource is present, not hidden, nor retired" do
       notification = create(:notification, notifiable: notifiable)
 
       expect(notification.notifiable_available?).to be true
@@ -30,7 +30,7 @@ shared_examples "notifiable" do
       expect(notification.notifiable_available?).to be true
     end
 
-    it "returns false when it's a root comment and the notifiable has been hidden" do
+    it "returns false if the resource is hidden" do
       notification = create(:notification, notifiable: notifiable)
 
       notifiable.hide
@@ -48,24 +48,12 @@ shared_examples "notifiable" do
 
       expect(notification.notifiable_available?).to be false
     end
-  end
-
-  describe "check_availability" do
-    it "returns true if the resource is present, not hidden, nor retired" do
-      notification = create(:notification, notifiable: notifiable)
-      expect(notification.check_availability(notifiable)).to be true
-    end
 
     it "returns false if the resource is not present" do
       notification = create(:notification, notifiable: notifiable)
       notifiable.really_destroy!
-      expect(notification.check_availability(notifiable)).to be false
-    end
 
-    it "returns false if the resource is not hidden" do
-      notification = create(:notification, notifiable: notifiable)
-      notifiable.hide
-      expect(notification.check_availability(notifiable)).to be false
+      expect(notification.notifiable_available?).to be false
     end
 
     it "returns false if the resource is retired" do
@@ -74,7 +62,7 @@ shared_examples "notifiable" do
       if notifiable.respond_to?(:retired_at)
         notifiable.update!(retired_at: Time.current, retired_reason: "unfeasible",
                            retired_explanation: "Unfeasibility explanation ...")
-        expect(notification.check_availability(notifiable)).to be false
+        expect(notification.notifiable_available?).to be false
       end
     end
   end