Enables RSpec/DescribedClass cop & fixes all issues

Autocorrection for existing issues, and stashing at .rubocop_todo.yml
the false positives

Read about cop at http://www.rubydoc.info/gems/rubocop-rspec/RuboCop/Cop/RSpec/DescribedClass

spec/models/activity_spec.rb

@@ -21,9 +21,9 @@ describe Activity do
       user = create(:user)
       proposal = create(:proposal)
 
-      expect{ Activity.log(user, :hide, proposal) }.to change { Activity.count }.by(1)
+      expect{ described_class.log(user, :hide, proposal) }.to change { described_class.count }.by(1)
 
-      activity = Activity.last
+      activity = described_class.last
       expect(activity.user_id).to eq(user.id)
       expect(activity.action).to eq("hide")
       expect(activity.actionable).to eq(proposal)
@@ -41,9 +41,9 @@ describe Activity do
       create(:activity, action: "hide", actionable: create(:comment))
       create(:activity, action: "block", actionable: create(:user))
 
-      expect(Activity.on(proposal).size).to eq 3
+      expect(described_class.on(proposal).size).to eq 3
       [activity1, activity2, activity3].each do |a|
-        expect(Activity.on(proposal)).to include(a)
+        expect(described_class.on(proposal)).to include(a)
       end
     end
   end
@@ -59,10 +59,10 @@ describe Activity do
       activity6 = create(:activity, user: user1, action: "valuate", actionable: create(:budget_investment))
       create_list(:activity, 3)
 
-      expect(Activity.by(user1).size).to eq 6
+      expect(described_class.by(user1).size).to eq 6
 
       [activity1, activity2, activity3, activity4, activity5, activity6].each do |a|
-        expect(Activity.by(user1)).to include(a)
+        expect(described_class.by(user1)).to include(a)
       end
     end
   end
@@ -75,17 +75,17 @@ describe Activity do
       on_user       = create(:activity, actionable: create(:user))
       on_investment = create(:activity, actionable: create(:budget_investment))
 
-      expect(Activity.on_proposals.size).to eq 1
-      expect(Activity.on_debates.size).to eq 1
-      expect(Activity.on_comments.size).to eq 1
-      expect(Activity.on_users.size).to eq 1
-      expect(Activity.on_budget_investments.size).to eq 1
+      expect(described_class.on_proposals.size).to eq 1
+      expect(described_class.on_debates.size).to eq 1
+      expect(described_class.on_comments.size).to eq 1
+      expect(described_class.on_users.size).to eq 1
+      expect(described_class.on_budget_investments.size).to eq 1
 
-      expect(Activity.on_proposals.first).to eq on_proposal
-      expect(Activity.on_debates.first).to eq on_debate
-      expect(Activity.on_comments.first).to eq on_comment
-      expect(Activity.on_users.first).to eq on_user
-      expect(Activity.on_budget_investments.first).to eq on_investment
+      expect(described_class.on_proposals.first).to eq on_proposal
+      expect(described_class.on_debates.first).to eq on_debate
+      expect(described_class.on_comments.first).to eq on_comment
+      expect(described_class.on_users.first).to eq on_user
+      expect(described_class.on_budget_investments.first).to eq on_investment
     end
   end