Add a Sidekiq retry size check

docs/healthchecks.md

@@ -131,3 +131,21 @@ class MySidekiqQueueSizeCheck < GovukHealthcheck::SidekiqQueueSizeCheck
   end
 end
 ```
+
+
+### `SidekiqRetrySizeCheck`
+
+Similar to `SidekiqQueueSizeCheck`, this class is the basis for a check which
+compares the Sidekiq retry set size with a warning and critical threshold.
+
+```ruby
+class MySidekiqRetrySizeCheck < GovukHealthcheck::SidekiqRetrySizeCheck
+  def warning_threshold
+    # the warning threshold for the retry set
+  end
+
+  def critical_threshold
+    # the critical threshold for the retry set
+  end
+end
+```

lib/govuk_app_config/govuk_healthcheck.rb

@@ -1,10 +1,11 @@
 require "govuk_app_config/govuk_healthcheck/checkup"
 require "govuk_app_config/govuk_healthcheck/active_record"
 require "govuk_app_config/govuk_healthcheck/sidekiq_redis"
+require "govuk_app_config/govuk_healthcheck/threshold_check"
 require "govuk_app_config/govuk_healthcheck/sidekiq_queue_check"
 require "govuk_app_config/govuk_healthcheck/sidekiq_queue_latency_check"
 require "govuk_app_config/govuk_healthcheck/sidekiq_queue_size_check"
-require "govuk_app_config/govuk_healthcheck/threshold_check"
+require "govuk_app_config/govuk_healthcheck/sidekiq_retry_size_check"
 require "json"
 
 module GovukHealthcheck

lib/govuk_app_config/govuk_healthcheck/sidekiq_retry_size_check.rb

@@ -0,0 +1,11 @@
+module GovukHealthcheck
+  class SidekiqRetrySizeCheck < ThresholdCheck
+    def name
+      :sidekiq_retry_size
+    end
+
+    def value
+      Sidekiq::Stats.new.retry_size
+    end
+  end
+end

spec/lib/govuk_healthcheck/sidekiq_retry_size_check_spec.rb

@@ -0,0 +1,27 @@
+require "spec_helper"
+require "govuk_app_config/govuk_healthcheck"
+require_relative "shared_interface"
+
+RSpec.describe GovukHealthcheck::SidekiqRetrySizeCheck do
+  subject { TestRetrySizeCheck.new }
+
+  let(:sidekiq_stats) { double(retry_size: 10) }
+  let(:sidekiq_stats_class) { double }
+
+  before do
+    allow(sidekiq_stats_class).to receive(:new).and_return(sidekiq_stats)
+    stub_const("Sidekiq::Stats", sidekiq_stats_class)
+  end
+
+  it_behaves_like "a healthcheck"
+
+  class TestRetrySizeCheck < GovukHealthcheck::SidekiqRetrySizeCheck
+    def warning_threshold
+      10
+    end
+
+    def critical_threshold
+      20
+    end
+  end
+end