handle the case of missing thread

lib/datadog/di/probe_notifier_worker.rb

@@ -91,10 +91,12 @@ def start
       def stop(timeout = 1)
         @stop_requested = true
         wake.signal
-        unless thread&.join(timeout)
-          thread.kill
+        if thread
+          unless thread.join(timeout)
+            thread.kill
+          end
+          @thread = nil
         end
-        @thread = nil
       end
 
       # Waits for background thread to send pending notifications.

spec/datadog/di/probe_notifier_worker_spec.rb

@@ -43,13 +43,27 @@
   end
 
   describe '#stop' do
-    before do
-      worker.start
+    context 'worker is running' do
+      before do
+        worker.start
+      end
+
+      it 'stops the thread' do
+        worker.stop
+        expect(worker.send(:thread)).to be nil
+      end
     end
 
-    it 'stops the thread' do
-      worker.stop
-      expect(worker.send(:thread)).to be nil
+    context 'worker is not running' do
+      before do
+        expect(worker.send(:thread)).to be nil
+      end
+
+      it 'does nothing and raises no exceptions' do
+        expect do
+          worker.stop
+        end.not_to raise_error
+      end
     end
   end