add more diagnostics for flaky spec

spec/components/scheduler/manager_spec.rb

@@ -61,6 +61,7 @@ describe Scheduler::Manager do
   before do
     expect(ActiveRecord::Base.connection_pool.connections.length).to eq(1)
     @thread_count = Thread.list.count
+    @thread_ids = Thread.list.map { |t| t.object_id }
   end
 
   after do
@@ -77,7 +78,29 @@ describe Scheduler::Manager do
       ActiveRecord::Base.connection_pool.remove(c)
     end
     expect(ActiveRecord::Base.connection_pool.connections.length).to eq(1)
-    wait_for do
+
+    on_thread_mismatch = lambda do
+      current = Thread.list.map { |t| t.object_id }
+
+      extra = current - @thread_ids
+      missing = @thread_ids - current
+
+      if missing.length > 0
+        STDERR.puts "\nMissing Threads #{missing.length} thread/s"
+      end
+
+      if extra.length > 0
+        Thread.list.each do |thread|
+          if extra.include?(thread.object_id)
+            STDERR.puts "\nExtra Thread Backtrace:"
+            STDERR.puts thread.backtrace
+            STDERR.puts
+          end
+        end
+      end
+    end
+
+    wait_for(on_fail: on_thread_mismatch) do
       @thread_count == Thread.list.count
     end
   end

spec/support/helpers.rb

@@ -61,7 +61,7 @@ module Helpers
     Guardian.stubs(new: guardian).with(user)
   end
 
-  def wait_for(&blk)
+  def wait_for(on_fail: nil, &blk)
     i = 0
     result = false
     while !result && i < 1000
@@ -70,6 +70,7 @@ module Helpers
       sleep 0.001
     end
 
+    on_fail&.call
     expect(result).to eq(true)
   end