Move and refactor method from follow to user model to get user interests. Add specification to check the discard of duplicate interests.

spec/models/user_spec.rb

@@ -657,4 +657,27 @@ describe User do
     end
   end
 
+  describe "#interests" do
+    let(:user)     { create(:user) }
+
+    it "should return followed object tags" do
+      proposal =  create(:proposal, tag_list: "Sport")
+      create(:follow, followable: proposal, user: user)
+
+      expect(user.interests).to eq ["Sport"]
+    end
+
+    it "should discard followed objects duplicated tags" do
+      proposal1 =  create(:proposal, tag_list: "Sport")
+      proposal2 =  create(:proposal, tag_list: "Sport")
+      budget_investment =  create(:budget_investment, tag_list: "Sport")
+
+      create(:follow, followable: proposal1, user: user)
+      create(:follow, followable: proposal2, user: user)
+      create(:follow, followable: budget_investment, user: user)
+
+      expect(user.interests).to eq ["Sport"]
+    end
+
+  end
 end