Add fork testing

lib/ddtrace/contrib/qless/patcher.rb

@@ -21,8 +21,8 @@ def patch
           # Instrument all Qless Workers
           ::Qless::Workers::BaseWorker.class_eval do
             # These are executed in inverse order of listing here
-            include TracerCleaner
             include QlessJob
+            include TracerCleaner
           end
         end
 

lib/ddtrace/contrib/qless/tracer_cleaner.rb

@@ -6,8 +6,9 @@ module TracerCleaner
         def around_perform(job)
           return super unless datadog_configuration && tracer
 
-          tracer.shutdown! if forked?
-          super
+          super.tap do
+            tracer.shutdown! if forked?
+          end
         end
 
         private

spec/ddtrace/contrib/qless/instrumentation_spec.rb

@@ -95,4 +95,50 @@
       end
     end
   end
+
+  context 'with forking' do
+    before do
+      # Ensures worker is using forking
+      expect(worker.class).to eq(Qless::Workers::ForkingWorker)
+    end
+
+    context 'trace context' do
+      subject(:perform) do
+        tracer.trace('parent.process') do |span|
+          @parent_span = span
+          perform_job(job_class)
+        end
+
+        expect(failed_jobs.count).to eq(0)
+      end
+
+      context 'on main process' do
+        it 'only contains parent process spans' do
+          perform
+
+          expect(span.name).to eq('parent.process')
+        end
+      end
+
+      context 'on child process' do
+        it 'does not include parent process spans' do
+          expect(job_class).to receive(:perform) do
+            # Mock #shutdown! in fork only
+            expect(tracer).to receive(:shutdown!).and_wrap_original do |m, *args|
+              m.call(*args)
+
+              expect(span.name).to eq('qless.job')
+              expect(span).to have_distributed_parent(@parent_span)
+            end
+          end
+
+          perform
+
+          # Remove hard-expectation from parent process,
+          # as `job_class#perform` won't be called in this process.
+          RSpec::Mocks.space.proxy_for(job_class).reset
+        end
+      end
+    end
+  end
 end

spec/support/span_helpers.rb

@@ -36,4 +36,17 @@ def description_of(actual) # rubocop:disable Lint/NestedMethodDefinition
   define_have_error_tag(:message, Datadog::Ext::Errors::MSG)
   define_have_error_tag(:stack, Datadog::Ext::Errors::STACK)
   define_have_error_tag(:type, Datadog::Ext::Errors::TYPE)
+
+  # Distributed traces have the same trace_id and parent_id as upstream parent
+  # span, but don't actually share the same Context with the parent.
+  RSpec::Matchers.define :have_distributed_parent do |parent|
+    match do |actual|
+      @matcher = have_attributes(parent_id: parent.span_id, trace_id: parent.trace_id)
+      @matcher.matches? actual
+    end
+
+    failure_message do
+      @matcher.failure_message
+    end
+  end
 end