Keep callbacks in an array and run each in turn until one returns nil

lib/govuk_app_config/govuk_error/configuration.rb

@@ -12,16 +12,15 @@ def initialize(_raven_configuration)
       @data_sync = GovukDataSync.new(ENV["GOVUK_DATA_SYNC_PERIOD"])
       self.active_sentry_environments = []
       self.data_sync_excluded_exceptions = []
-      super.before_send = default_before_send_actions
+      @before_send_callbacks = [
+        ignore_exceptions_based_on_env_and_data_sync,
+        increment_govuk_statsd_counters,
+      ]
+      super.before_send = run_before_send_callbacks
     end
 
     def before_send=(closure)
-      combined = lambda do |error_or_event, hint|
-        default_before_send_actions.call(error_or_event, hint) &&
-          closure.call(error_or_event, hint)
-      end
-
-      super(combined)
+      @before_send_callbacks.insert(-2, closure)
     end
 
   protected
@@ -61,9 +60,12 @@ def increment_govuk_statsd_counters
       }
     end
 
-    def default_before_send_actions
+    def run_before_send_callbacks
       lambda do |error_or_event, hint|
-        (ignore_exceptions_based_on_env_and_data_sync.call(error_or_event, hint) && increment_govuk_statsd_counters.call(error_or_event, hint))
+        @before_send_callbacks.each do |callback|
+          break if callback.call(error_or_event, hint).nil?
+        end
+        error_or_event
       end
     end
   end

spec/govuk_error/configuration_spec.rb

@@ -121,30 +121,33 @@
           expect(GovukStatsd).to receive(:increment).exactly(1).times.with("error_types.standard_error")
           expect(GovukStatsd).to receive(:increment).exactly(1).times.with("hello_world")
 
-          configuration.before_send = lambda do |_error_or_event, _hint|
+          configuration.before_send = lambda do |error_or_event, _hint|
             GovukStatsd.increment("hello_world")
+            error_or_event
           end
 
           configuration.before_send.call(StandardError.new)
         end
       end
     end
 
-    context "when the before_send lambda has been overridden twice, the first does not take effect" do
+    context "when the before_send lambda has been overridden several times, all take effect" do
       before { stub_const("GovukStatsd", double(Module)) }
       it "increments the appropriate counters" do
         ClimateControl.modify SENTRY_CURRENT_ENV: "production" do
           configuration.active_sentry_environments << "production"
           expect(GovukStatsd).to receive(:increment).exactly(1).times.with("errors_occurred")
           expect(GovukStatsd).to receive(:increment).exactly(1).times.with("error_types.standard_error")
-          expect(GovukStatsd).not_to receive(:increment).with("does_not_happen")
           expect(GovukStatsd).to receive(:increment).exactly(1).times.with("hello_world")
+          expect(GovukStatsd).to receive(:increment).exactly(1).times.with("hello_world_again")
 
-          configuration.before_send = lambda do |_error_or_event, _hint|
-            GovukStatsd.increment("does_not_happen")
-          end
-          configuration.before_send = lambda do |_error_or_event, _hint|
+          configuration.before_send = lambda do |error_or_event, _hint|
             GovukStatsd.increment("hello_world")
+            error_or_event
+          end
+          configuration.before_send = lambda do |error_or_event, _hint|
+            GovukStatsd.increment("hello_world_again")
+            error_or_event
           end
 
           configuration.before_send.call(StandardError.new)
@@ -159,11 +162,26 @@
         raven_configurator = GovukError::Configuration.new(Raven.configuration)
         raven_configurator.active_sentry_environments << "production"
         raven_configurator.before_send = lambda do |error_or_event, _hint|
-          error_or_event == "do capture"
+          error_or_event if error_or_event == "do capture"
         end
 
         expect(raven_configurator.before_send.call("do capture")).to be_truthy
-        expect(raven_configurator.before_send.call("don't capture", {})).to be false
+        expect(raven_configurator.before_send.call("don't capture", {})).to be_nil
+      end
+    end
+
+    it "does not increment the counters if the callback returns nil" do
+      ClimateControl.modify SENTRY_CURRENT_ENV: "production" do
+        raven_configurator = GovukError::Configuration.new(Raven.configuration)
+        raven_configurator.active_sentry_environments << "production"
+        raven_configurator.before_send = lambda do |_error_or_event, _hint|
+          nil
+        end
+
+        expect(GovukStatsd).not_to receive(:increment).with("errors_occurred")
+        expect(GovukStatsd).not_to receive(:increment).with("error_types.standard_error")
+
+        raven_configurator.before_send.call(StandardError.new)
       end
     end
   end