fix: Do not log error when there are no metrics to export (#1953)

* Fix debug logging when there are no metrics to export

When collected_metrics is empty, result_code was not getting set and so report_result would fail.

Reported by: @utay

Related to: #1947 and #1888

* use case statement

* do not log errors

* Favor modifier if usage when having a single-line body.

Author: wsmoak

metrics_sdk/lib/opentelemetry/sdk/metrics/export/periodic_metric_reader.rb

@@ -130,12 +130,7 @@ def export(timeout: nil)
           end
 
           def report_result(result_code)
-            if result_code == Export::SUCCESS
-              OpenTelemetry.logger.debug 'Successfully exported metrics'
-            else
-              OpenTelemetry.handle_error(exception: ExportError.new('Unable to export metrics'))
-              OpenTelemetry.logger.error("Result code: #{result_code}")
-            end
+            OpenTelemetry.logger.debug 'Successfully exported metrics' if result_code == Export::SUCCESS
           end
 
           def lock(&block)

metrics_sdk/test/opentelemetry/sdk/metrics/export/periodic_metric_reader_test.rb

@@ -9,8 +9,6 @@
 describe OpenTelemetry::SDK::Metrics::Export::PeriodicMetricReader do
   PeriodicMetricReader = OpenTelemetry::SDK::Metrics::Export::PeriodicMetricReader
   SUCCESS = OpenTelemetry::SDK::Metrics::Export::SUCCESS
-  FAILURE = OpenTelemetry::SDK::Metrics::Export::FAILURE
-  TIMEOUT = OpenTelemetry::SDK::Metrics::Export::TIMEOUT
 
   class TestExporter
     def initialize(status_codes: nil)
@@ -35,27 +33,6 @@ def shutdown(timeout: nil) = SUCCESS
     def force_flush(timeout: nil) = SUCCESS
   end
 
-  describe 'exporter with failure' do
-    let(:exporter) { TestExporter.new(status_codes: [FAILURE]) }
-    let(:reader) { PeriodicMetricReader.new(exporter: exporter) }
-
-    it 'logs export failure as error' do
-      mock_logger = Minitest::Mock.new
-      mock_logger.expect(:error, nil, [/Unable to export metrics/])
-      mock_logger.expect(:error, nil, [/Result code: 1/])
-
-      # Stub collect to return a non-empty array so export is actually called
-      reader.stub(:collect, ['mock_metric']) do
-        OpenTelemetry.stub(:logger, mock_logger) do
-          reader.force_flush
-        end
-      end
-
-      reader.shutdown
-      mock_logger.verify
-    end
-  end
-
   describe 'succesful exporter' do
     let(:exporter) { TestExporter.new(status_codes: [SUCCESS]) }
     let(:reader) { PeriodicMetricReader.new(exporter: exporter) }