Fix: Accomodate apps that do not use Sidekiq Enterprise (#42)

* Fix: Accomodate apps that do not use Sidekiq Enterprise

Why?
====

Apps that do not use Sidekiq Enterprise will not have a `Sidekiq::Limiter` module defined. As a
result, if an error is encountered while in the `#call` method of `SidekiqPrometheus::JobMetrics`
then an additional problem will be encountered, causing a large backlog of errors re-enqueueing into
Sidekiq.

What?
=====

1. Wrap the specs in following proper contexts:
   * That Sidekiq Enterprise error class exists. And...
   * That error class does NOT exist.
2. Test that the correct behavior occurs in those two contexts.
3. Lastly, in the implementation code, make sure we ask that we check for presence of
   `Sidekiq::Limiter::OverLimit`

* rake standard:fix

---------

Co-authored-by: Lukas Eklund <leklund@fastly.com>

lib/sidekiq_prometheus/job_metrics.rb

@@ -30,7 +30,7 @@ def call(worker, job, queue)
 
       result
     rescue => e
-      if e.instance_of?(::Sidekiq::Limiter::OverLimit)
+      if defined?(::Sidekiq::Limiter::OverLimit) && e.instance_of?(::Sidekiq::Limiter::OverLimit)
         registry[:sidekiq_job_over_limit].increment(labels: labels)
       else
         err_label = {error_class: e.class.to_s}

spec/sidekiq_prometheus/job_metrics_spec.rb

@@ -8,11 +8,6 @@ def prometheus_labels
   end
 end
 
-module Sidekiq::Limiter
-  class OverLimit < StandardError
-  end
-end
-
 RSpec.describe SidekiqPrometheus::JobMetrics do
   let(:middleware) { described_class.new }
   let(:registry) { instance_double Prometheus::Client::Registry }
@@ -28,81 +23,121 @@ class OverLimit < StandardError
   end
 
   describe "#call" do
-    it "records the expected metrics" do
-      SidekiqPrometheus.registry = registry
-      allow(registry).to receive(:get).and_return(metric)
+    context "when Sidekiq::Limiter module is not defined" do
+      before do
+        # Ensure that if this module _is_ defined (depending on random spec
+        # execution order) that we remove it so we can test the fallback
+        # behavior.
+        if defined?(Sidekiq::Limiter)
+          Sidekiq.send(:remove_const, :Limiter)
+        end
+      end
 
-      expect { |b| middleware.call(worker, job, queue, &b) }.to yield_control
+      it "handles other errors with the fallback sidekiq_job_failed metric" do
+        SidekiqPrometheus.registry = registry
+        allow(registry).to receive(:get).and_return(metric)
 
-      expect(registry).to have_received(:get).with(:sidekiq_job_count)
-      expect(registry).to have_received(:get).with(:sidekiq_job_duration)
-      expect(registry).to have_received(:get).with(:sidekiq_job_success)
-      expect(registry).to have_received(:get).with(:sidekiq_job_allocated_objects)
+        expect { middleware.call(worker, job, queue) { raise StandardError } }.to raise_error(StandardError)
 
-      expect(metric).to have_received(:increment).twice.with(labels: labels)
-      expect(metric).to have_received(:observe).twice.with(kind_of(Numeric), labels: labels)
+        expect(registry).not_to have_received(:get).with(:sidekiq_job_over_limit)
+        expect(registry).to have_received(:get).with(:sidekiq_job_count)
+        expect(registry).to have_received(:get).with(:sidekiq_job_failed)
+
+        expect(registry).not_to have_received(:get).with(:sidekiq_job_duration)
+        expect(registry).not_to have_received(:get).with(:sidekiq_job_success)
+
+        expect(metric).to have_received(:increment).once.with(labels: labels)
+        expect(metric).to have_received(:increment).once.with(labels: labels.merge(error_class: "StandardError"))
+        expect(metric).not_to have_received(:observe)
+      end
     end
 
-    it "returns the result from the yielded block" do
-      SidekiqPrometheus.registry = registry
-      allow(registry).to receive(:get).and_return(metric)
-      expected = "Zoot Boot"
+    context "when Sidekiq::Limiter::OverLimit class is defined" do
+      before do
+        unless defined?(Sidekiq::Limiter::OverLimit)
+          module Sidekiq::Limiter
+            class OverLimit < StandardError
+            end
+          end
+        end
+      end
 
-      result = middleware.call(worker, job, queue) { expected }
+      it "records the expected metrics" do
+        SidekiqPrometheus.registry = registry
+        allow(registry).to receive(:get).and_return(metric)
 
-      expect(result).to eq(expected)
-    end
+        expect { |b| middleware.call(worker, job, queue, &b) }.to yield_control
 
-    it "increments the sidekiq_job_failed metric on error and raises" do
-      SidekiqPrometheus.registry = registry
-      allow(registry).to receive(:get).and_return(metric)
+        expect(registry).to have_received(:get).with(:sidekiq_job_count)
+        expect(registry).to have_received(:get).with(:sidekiq_job_duration)
+        expect(registry).to have_received(:get).with(:sidekiq_job_success)
+        expect(registry).to have_received(:get).with(:sidekiq_job_allocated_objects)
 
-      expect { middleware.call(worker, job, queue) { raise "no way!" } }.to raise_error(StandardError)
+        expect(metric).to have_received(:increment).twice.with(labels: labels)
+        expect(metric).to have_received(:observe).twice.with(kind_of(Numeric), labels: labels)
+      end
 
-      expect(registry).to have_received(:get).with(:sidekiq_job_count)
-      expect(registry).to have_received(:get).with(:sidekiq_job_failed)
-      expect(registry).not_to have_received(:get).with(:sidekiq_job_duration)
-      expect(registry).not_to have_received(:get).with(:sidekiq_job_success)
+      it "returns the result from the yielded block" do
+        SidekiqPrometheus.registry = registry
+        allow(registry).to receive(:get).and_return(metric)
+        expected = "Zoot Boot"
 
-      expect(metric).to have_received(:increment).once.with(labels: failed_labels)
-      expect(metric).to have_received(:increment).once.with(labels: labels)
-      expect(metric).not_to have_received(:observe)
-    end
+        result = middleware.call(worker, job, queue) { expected }
 
-    it "handles sidekiq ent Sidekiq::Limiter::OverLimit errors independently of failures" do
-      SidekiqPrometheus.registry = registry
-      allow(registry).to receive(:get).and_return(metric)
+        expect(result).to eq(expected)
+      end
 
-      expect { middleware.call(worker, job, queue) { raise Sidekiq::Limiter::OverLimit } }.to raise_error(Sidekiq::Limiter::OverLimit)
+      it "increments the sidekiq_job_failed metric on error and raises" do
+        SidekiqPrometheus.registry = registry
+        allow(registry).to receive(:get).and_return(metric)
 
-      expect(registry).to have_received(:get).with(:sidekiq_job_count)
-      expect(registry).to have_received(:get).with(:sidekiq_job_over_limit)
-      expect(registry).not_to have_received(:get).with(:sidekiq_job_failed)
-      expect(registry).not_to have_received(:get).with(:sidekiq_job_duration)
-      expect(registry).not_to have_received(:get).with(:sidekiq_job_success)
+        expect { middleware.call(worker, job, queue) { raise "no way!" } }.to raise_error(StandardError)
 
-      expect(metric).to have_received(:increment).twice.with(labels: labels)
-      expect(metric).not_to have_received(:observe)
-    end
+        expect(registry).to have_received(:get).with(:sidekiq_job_count)
+        expect(registry).to have_received(:get).with(:sidekiq_job_failed)
+        expect(registry).not_to have_received(:get).with(:sidekiq_job_duration)
+        expect(registry).not_to have_received(:get).with(:sidekiq_job_success)
 
-    context "when worker class is ActiveJob::QueueAdapters::SidekiqAdapter::JobWrapper" do
-      let(:wrapped_class) { "WrappedActiveJobClass" }
-      let(:job) { {"wrapped" => wrapped_class} }
-      let(:labels) { {class: wrapped_class, queue: queue, foo: "bar"} }
+        expect(metric).to have_received(:increment).once.with(labels: failed_labels)
+        expect(metric).to have_received(:increment).once.with(labels: labels)
+        expect(metric).not_to have_received(:observe)
+      end
 
-      it "sets the metric class attribute to the wrapped class" do
+      it "handles sidekiq ent Sidekiq::Limiter::OverLimit errors independently of failures" do
         SidekiqPrometheus.registry = registry
         allow(registry).to receive(:get).and_return(metric)
 
-        expect { |b| middleware.call(worker, job, queue, &b) }.to yield_control
+        expect { middleware.call(worker, job, queue) { raise Sidekiq::Limiter::OverLimit } }.to raise_error(Sidekiq::Limiter::OverLimit)
 
         expect(registry).to have_received(:get).with(:sidekiq_job_count)
-        expect(registry).to have_received(:get).with(:sidekiq_job_duration)
-        expect(registry).to have_received(:get).with(:sidekiq_job_success)
-        expect(registry).to have_received(:get).with(:sidekiq_job_allocated_objects)
+        expect(registry).to have_received(:get).with(:sidekiq_job_over_limit)
+        expect(registry).not_to have_received(:get).with(:sidekiq_job_failed)
+        expect(registry).not_to have_received(:get).with(:sidekiq_job_duration)
+        expect(registry).not_to have_received(:get).with(:sidekiq_job_success)
 
         expect(metric).to have_received(:increment).twice.with(labels: labels)
-        expect(metric).to have_received(:observe).twice.with(kind_of(Numeric), labels: labels)
+        expect(metric).not_to have_received(:observe)
+      end
+
+      context "when worker class is ActiveJob::QueueAdapters::SidekiqAdapter::JobWrapper" do
+        let(:wrapped_class) { "WrappedActiveJobClass" }
+        let(:job) { {"wrapped" => wrapped_class} }
+        let(:labels) { {class: wrapped_class, queue: queue, foo: "bar"} }
+
+        it "sets the metric class attribute to the wrapped class" do
+          SidekiqPrometheus.registry = registry
+          allow(registry).to receive(:get).and_return(metric)
+
+          expect { |b| middleware.call(worker, job, queue, &b) }.to yield_control
+
+          expect(registry).to have_received(:get).with(:sidekiq_job_count)
+          expect(registry).to have_received(:get).with(:sidekiq_job_duration)
+          expect(registry).to have_received(:get).with(:sidekiq_job_success)
+          expect(registry).to have_received(:get).with(:sidekiq_job_allocated_objects)
+
+          expect(metric).to have_received(:increment).twice.with(labels: labels)
+          expect(metric).to have_received(:observe).twice.with(kind_of(Numeric), labels: labels)
+        end
       end
     end
   end