Add unit test for callbacks

spec/ddtrace/workers_spec.rb

@@ -0,0 +1,23 @@
+require 'spec_helper'
+
+RSpec.describe Datadog::Workers::AsyncTransport do
+  describe 'callbacks' do
+    describe 'when raising errors' do
+      it 'does not re-raise' do
+        buf = StringIO.new
+        Datadog::Tracer.log = Datadog::Logger.new(buf)
+        task = proc { raise StandardError }
+        worker = Datadog::Workers::AsyncTransport.new(nil, 100, task, task, 0.5)
+
+        worker.enqueue_trace(get_test_traces(1))
+        worker.enqueue_service(get_test_services)
+
+        expect { worker.callback_traces }.to_not raise_error
+        expect { worker.callback_services }.to_not raise_error
+
+        lines = buf.string.lines
+        expect(lines.length).to eq 2
+      end
+    end
+  end
+end