Deprecate StreamingListener middleware

Deprecate the StreamingListener now that it is almost identical to the
AbstractMiddleware. Those couple differences are actually ones we don't
want people to rely on, so deprecate it.

.changesets/deprecate-appsignal--rack--streaminglistener-middleware.md

@@ -0,0 +1,7 @@
+---
+bump: patch
+type: deprecate
+---
+
+Deprecate the `Appsignal::Rack::StreamingListener` middleware. Use the `Appsignal::Rack::InstrumentationMiddleware` middleware instead.
+

lib/appsignal/rack/streaming_listener.rb

@@ -1,5 +1,10 @@
 # frozen_string_literal: true
 
+Appsignal::Utils::StdoutAndLoggerMessage.warning \
+  "The constant Appsignal::Rack::StreamingListener has been deprecated. " \
+    "Please update the constant name to " \
+    "Appsignal::Rack::InstrumentationMiddleware."
+
 module Appsignal
   module Rack
     # Instrumentation middleware that tracks exceptions in streaming Rack

spec/lib/appsignal/rack/streaming_listener_spec.rb

@@ -1,33 +1,69 @@
-require "appsignal/rack/streaming_listener"
+describe "Appsignal::Rack::StreamingListener" do
+  def load_middleware
+    load "lib/appsignal/rack/streaming_listener.rb"
+  end
 
-describe Appsignal::Rack::StreamingListener do
-  let(:env) { {} }
-  let(:app) { DummyApp.new }
-  let(:middleware) { described_class.new(app, {}) }
-  before { start_agent }
-  around { |example| keep_transactions { example.run } }
+  describe "loading the streaming_listener integrations file" do
+    let(:err_stream) { std_stream }
+    let(:stderr) { err_stream.read }
+    after { Appsignal::Rack.send(:remove_const, :StreamingListener) }
 
-  def make_request
-    middleware.call(env)
-  end
+    it "prints a deprecation warning to STDERR" do
+      capture_std_streams(std_stream, err_stream) do
+        load_middleware
+      end
 
-  it "instruments the call" do
-    make_request
+      expect(stderr).to include(
+        "appsignal WARNING: The constant Appsignal::Rack::StreamingListener " \
+          "has been deprecated."
+      )
+    end
 
-    expect(last_transaction).to include_event("name" => "process_streaming_request.rack")
+    it "logs a warning" do
+      logs =
+        capture_logs do
+          silence do
+            load_middleware
+          end
+        end
+
+      expect(logs).to contains_log(
+        :warn,
+        "The constant Appsignal::Rack::StreamingListener has been deprecated."
+      )
+    end
   end
 
-  it "set no action by default" do
-    make_request
+  describe "middleware" do
+    let(:env) { {} }
+    let(:app) { DummyApp.new }
+    let(:middleware) { Appsignal::Rack::StreamingListener.new(app, {}) }
+    around { |example| keep_transactions { example.run } }
+    before(:context) { load_middleware }
+    before { start_agent }
 
-    expect(last_transaction).to_not have_action
-  end
+    def make_request
+      middleware.call(env)
+    end
+
+    it "instruments the call" do
+      make_request
+
+      expect(last_transaction).to include_event("name" => "process_streaming_request.rack")
+    end
+
+    it "set no action by default" do
+      make_request
+
+      expect(last_transaction).to_not have_action
+    end
 
-  it "set `appsignal.action` to the action name" do
-    env["appsignal.action"] = "Action"
+    it "set `appsignal.action` to the action name" do
+      env["appsignal.action"] = "Action"
 
-    make_request
+      make_request
 
-    expect(last_transaction).to have_action("Action")
+      expect(last_transaction).to have_action("Action")
+    end
   end
 end