Fallback to the default zone when a zone can't be found

Previously we would only use the default if no parameter was give. If a parameter was a given that didn't match any zone, we return an empty result and this would cause problems.

We now default to the default zone when a zone cannot be found.

app/controllers/forecasts_controller.rb

@@ -48,9 +48,9 @@ def forecast_for_day(day, forecasts)
   end
 
   def zone
-    return Zone.default unless params[:zone]
-
-    Zone.find_by(name: params[:zone])
+    Zone.find_by!(name: params[:zone])
+  rescue ActiveRecord::RecordNotFound
+    Zone.default
   end
 
   def date

spec/controllers/forecasts_controller_spec.rb

@@ -3,7 +3,6 @@
   let(:barnet) { double("Barnet") }
 
   before do
-    allow(Zone).to receive(:find_by).and_return(barnet)
     allow(Zone).to receive(:default).and_return(central_london)
     allow(CercForecastService).to receive(:latest_forecasts_for).and_return(forecasts)
   end
@@ -23,7 +22,9 @@
 
     context "when zone IS given" do
       it "obtains forecasts for the given zone from the CercForecastService" do
-        get :show, params: {zone: double}
+        allow(Zone).to receive(:find_by).and_return(barnet)
+
+        get :show, params: {zone: "Barnet"}
 
         expect(CercForecastService).to have_received(:latest_forecasts_for).with(barnet)
       end