Ensure Sidekiq client middleware is same for clients & servers

lib/ddtrace/contrib/sidekiq/patcher.rb

@@ -15,14 +15,21 @@ def target_version
 
         def patch
           require 'ddtrace/contrib/sidekiq/client_tracer'
+          require 'ddtrace/contrib/sidekiq/server_tracer'
+
           ::Sidekiq.configure_client do |config|
             config.client_middleware do |chain|
               chain.add(Sidekiq::ClientTracer)
             end
           end
 
-          require 'ddtrace/contrib/sidekiq/server_tracer'
           ::Sidekiq.configure_server do |config|
+            # If a job enqueues another job, make sure it has the same client
+            # middleware.
+            config.client_middleware do |chain|
+              chain.add(Sidekiq::ClientTracer)
+            end
+
             config.server_middleware do |chain|
               chain.add(Sidekiq::ServerTracer)
             end

spec/ddtrace/contrib/sidekiq/patcher_spec.rb

@@ -0,0 +1,35 @@
+require 'ddtrace/contrib/support/spec_helper'
+require_relative 'support/helper'
+
+RSpec.describe Datadog::Contrib::Sidekiq::Patcher do
+  before do
+    Sidekiq.client_middleware.clear
+    Sidekiq.server_middleware.clear
+
+    allow(Sidekiq).to receive(:server?).and_return(server)
+    # NB: This is needed because we want to patch multiple times.
+    allow(described_class).to receive(:do_once).with(:patch).and_yield
+  end
+
+  # NB: This needs to be after the before block above so that the use :sidekiq
+  # executes after the allows are setup.
+  include_context 'Sidekiq testing'
+
+  context 'for a client' do
+    let(:server) { false }
+
+    it 'correctly patches' do
+      expect(Sidekiq.client_middleware.entries.map(&:klass)).to eq([Datadog::Contrib::Sidekiq::ClientTracer])
+      expect(Sidekiq.server_middleware.entries.map(&:klass)).to eq([])
+    end
+  end
+
+  context 'for a server' do
+    let(:server) { true }
+
+    it 'correctly patches' do
+      expect(Sidekiq.client_middleware.entries.map(&:klass)).to eq([Datadog::Contrib::Sidekiq::ClientTracer])
+      expect(Sidekiq.server_middleware.entries.map(&:klass)).to eq([Datadog::Contrib::Sidekiq::ServerTracer])
+    end
+  end
+end