Don't start again in Hanami integration

When AppSignal is already active, do not start AppSignal again.
This is a good precaution as it prevents boot loops, when AppSignal is
started twice with different configurations.

This will improve support for nested Hanami applications, when they're
mounted in another frameworks we support, like Rails or Sinatra.

This is similar to PR #1105

Part of #329

.changesets/don-t-start-for-hanami-if-already-started.md

@@ -0,0 +1,7 @@
+---
+bump: patch
+type: fix
+---
+
+Fix issue with AppSignal getting stuck in a boot loop when loading the Hanami integration with: `require "appsignal/integrations/hanami"`
+This could happen in nested applications, like a Hanami app in a Rails app. It will now use the first config AppSignal starts with.

lib/appsignal/integrations/hanami.rb

@@ -11,12 +11,14 @@ def self.init
         Appsignal.internal_logger.debug("Loading Hanami integration")
 
         hanami_app_config = ::Hanami.app.config
-        Appsignal.config = Appsignal::Config.new(
-          hanami_app_config.root || Dir.pwd,
-          hanami_app_config.env
-        )
 
-        Appsignal.start
+        unless Appsignal.active?
+          Appsignal.config = Appsignal::Config.new(
+            hanami_app_config.root || Dir.pwd,
+            hanami_app_config.env
+          )
+          Appsignal.start
+        end
 
         return unless Appsignal.active?
 

spec/lib/appsignal/integrations/hanami_spec.rb

@@ -74,6 +74,39 @@ def uninstall_hanami_middleware
         end
       end
 
+      context "when AppSignal is already active" do
+        before do
+          expect(Appsignal).to receive(:active?).at_least(1).and_return(true)
+        end
+
+        it "does not initialize AppSignal again" do
+          expect(Appsignal).to_not receive(:start)
+
+          Appsignal::Integrations::HanamiPlugin.init
+        end
+
+        it "prepends the integration to Hanami::Action" do
+          Appsignal::Integrations::HanamiPlugin.init
+
+          expect(::Hanami::Action)
+            .to have_received(:prepend).with(Appsignal::Integrations::HanamiIntegration)
+        end
+
+        it "adds middleware to the Hanami app" do
+          Appsignal::Integrations::HanamiPlugin.init
+
+          expect(::Hanami.app.config.middleware.stack[::Hanami::Router::DEFAULT_PREFIX])
+            .to include(
+              [
+                Rack::Events,
+                [[kind_of(Appsignal::Rack::EventHandler)]],
+                *hanami_middleware_options
+              ],
+              [Appsignal::Rack::HanamiMiddleware, [], *hanami_middleware_options]
+            )
+        end
+      end
+
       context "when APPSIGNAL_APP_ENV ENV var is provided" do
         it "uses this as the environment" do
           ENV["APPSIGNAL_APP_ENV"] = "custom"