Refactor usage data counters specs

This makes these tests available for other implementations

spec/lib/gitlab/usage_data_counters/wiki_page_counter_spec.rb

@@ -2,68 +2,13 @@
 
 require 'spec_helper'
 
-describe Gitlab::UsageDataCounters::WikiPageCounter, :clean_gitlab_redis_shared_state do
-  shared_examples :wiki_page_event do |event|
-    describe ".count(#{event})" do
-      it "increments the wiki page #{event} counter by 1" do
-        expect do
-          described_class.count(event)
-        end.to change { described_class.read(event) }.by 1
-      end
-    end
-
-    describe ".read(#{event})" do
-      event_count = 5
-
-      it "returns the total number of #{event} events" do
-        event_count.times do
-          described_class.count(event)
-        end
-
-        expect(described_class.read(event)).to eq(event_count)
-      end
-    end
-  end
-
-  include_examples :wiki_page_event, :create
-  include_examples :wiki_page_event, :update
-  include_examples :wiki_page_event, :delete
-
-  describe 'totals' do
-    creations = 5
-    edits = 3
-    deletions = 2
-
-    before do
-      creations.times do
-        described_class.count(:create)
-      end
-      edits.times do
-        described_class.count(:update)
-      end
-      deletions.times do
-        described_class.count(:delete)
-      end
-    end
-
-    it 'can report all totals' do
-      expect(described_class.totals).to include(
-        wiki_pages_update: edits,
-        wiki_pages_create: creations,
-        wiki_pages_delete: deletions
-      )
-    end
-  end
-
-  describe 'unknown events' do
-    error = described_class::UnknownEvent
-
-    it 'cannot increment' do
-      expect { described_class.count(:wibble) }.to raise_error error
-    end
-
-    it 'cannot read' do
-      expect { described_class.read(:wibble) }.to raise_error error
-    end
-  end
+describe Gitlab::UsageDataCounters::WikiPageCounter do
+  it_behaves_like 'a redis usage counter', 'Wiki Page', :create
+  it_behaves_like 'a redis usage counter', 'Wiki Page', :update
+  it_behaves_like 'a redis usage counter', 'Wiki Page', :delete
+
+  it_behaves_like 'a redis usage counter with totals', :wiki_pages,
+    create: 5,
+    update: 3,
+    delete: 2
 end

spec/support/shared_examples/lib/gitlab/usage_data_counters/a_redis_counter.rb

+# frozen_string_literal: true
+
+shared_examples 'a redis usage counter' do |thing, event|
+  describe ".count(#{event})", :clean_gitlab_redis_shared_state do
+    it "increments the #{thing} #{event} counter by 1" do
+      expect do
+        described_class.count(event)
+      end.to change { described_class.read(event) }.by 1
+    end
+  end
+
+  describe ".read(#{event})", :clean_gitlab_redis_shared_state do
+    event_count = 5
+
+    it "returns the total number of #{event} events" do
+      event_count.times do
+        described_class.count(event)
+      end
+
+      expect(described_class.read(event)).to eq(event_count)
+    end
+  end
+end
+
+shared_examples 'a redis usage counter with totals' do |prefix, events|
+  describe 'totals', :clean_gitlab_redis_shared_state do
+    before do
+      events.each do |k, n|
+        n.times do
+          described_class.count(k)
+        end
+      end
+    end
+
+    let(:expected_totals) do
+      events.transform_keys { |k| "#{prefix}_#{k}".to_sym }
+    end
+
+    it 'can report all totals' do
+      expect(described_class.totals).to include(expected_totals)
+    end
+  end
+
+  # Override these let-bindings to adjust the unknown events tests
+  let(:unknown_event) { described_class::UnknownEvent }
+  let(:bad_event) { :wibble }
+
+  describe 'unknown events' do
+    it 'cannot increment' do
+      expect { described_class.count(bad_event) }.to raise_error unknown_event
+    end
+
+    it 'cannot read' do
+      expect { described_class.read(bad_event) }.to raise_error unknown_event
+    end
+  end
+end