feat: default tracer prototype

api/lib/opentelemetry.rb

@@ -35,6 +35,13 @@ def tracer_provider
     @tracer_provider ||= Trace::TracerProvider.new
   end
 
+  # @return [Trace::Tracer] delegates to the registered tracer provider and
+  #  returns a tracer with the given name and version. If called without without
+  #  arguments, it returns an unnamed default tracer.
+  def tracer(name = nil, version = nil)
+    tracer_provider.tracer(name, version)
+  end
+
   # @return [Object, Metrics::MeterProvider] registered meter provider or a
   #   default no-op implementation of the meter provider.
   def meter_provider

api/test/opentelemetry_test.rb

@@ -30,6 +30,45 @@
     end
   end
 
+  describe '.tracer' do
+    let(:mock_provider) { MiniTest::Mock.new }
+
+    after do
+      # Ensure we don't leak custom tracer factories and tracers to other tests
+      OpenTelemetry.tracer_provider = nil
+    end
+
+    describe 'default tracer' do
+      it 'returns the same instance when accessed multiple times' do
+        _(OpenTelemetry.tracer).must_equal(OpenTelemetry.tracer)
+      end
+    end
+
+    describe 'delegation' do
+      before do
+        OpenTelemetry.tracer_provider = mock_provider
+      end
+
+      it 'delegates to tracer provider' do
+        mock_provider.expect(:tracer, Object.new, [nil, nil])
+        _ = OpenTelemetry.tracer
+        mock_provider.verify
+      end
+
+      it 'delegates to tracer provider with provided name' do
+        mock_provider.expect(:tracer, Object.new, ['foo', nil])
+        _ = OpenTelemetry.tracer('foo')
+        mock_provider.verify
+      end
+
+      it 'delegates to tracer provider with provided name and version' do
+        mock_provider.expect(:tracer, Object.new, ['foo', '0.4.0'])
+        _ = OpenTelemetry.tracer('foo', '0.4.0')
+        mock_provider.verify
+      end
+    end
+  end
+
   describe '.logger' do
     it 'should log things' do
       t = Tempfile.new('logger')