Add rake task to remove duplicated local census records

Also supress migration messages during spec execution to keep test log as clean
as possible.

lib/tasks/local_census_records.rake

@@ -0,0 +1,13 @@
+namespace :local_census_records do
+  desc "Remove duplicated records from database"
+  task remove_duplicates: :environment do
+    ids = LocalCensusRecord.group(:document_type, :document_number).pluck("MIN(id) as id")
+    duplicates = LocalCensusRecord.count - ids.size
+
+    if duplicates > 0
+      ApplicationLogger.new.info "Removing local census records duplicates"
+      LocalCensusRecord.where("id NOT IN (?)", ids).destroy_all
+      ApplicationLogger.new.info "Removed #{duplicates} records."
+    end
+  end
+end

spec/lib/tasks/local_census_records_spec.rb

@@ -0,0 +1,36 @@
+require "rails_helper"
+require Rails.root.join("db", "migrate", "20190530082138_add_unique_index_to_local_census_records")
+
+describe "LocalCensusRecord tasks" do
+  let(:run_rake_task) do
+    Rake::Task["local_census_records:remove_duplicates"].reenable
+    Rake.application.invoke_task("local_census_records:remove_duplicates")
+  end
+
+  describe "#remove_duplicates" do
+    around do |example|
+      ActiveRecord::Migration.suppress_messages do
+        example.run
+      end
+    end
+
+    before { AddUniqueIndexToLocalCensusRecords.new.down }
+    after { AddUniqueIndexToLocalCensusRecords.new.up }
+
+    it "Remove all duplicates keeping older records" do
+      record1 = create(:local_census_record, document_type: "1", document_number: "#DOCUMENT_NUMBER")
+      record2 = create(:local_census_record, document_type: "2", document_number: "#DOCUMENT_NUMBER")
+      dup_record1 = build(:local_census_record, document_type: "1", document_number: "#DOCUMENT_NUMBER")
+      dup_record1.save!(validate: false)
+      dup_record2 = build(:local_census_record, document_type: "2", document_number: "#DOCUMENT_NUMBER")
+      dup_record2.save!(validate: false)
+      record3 = create(:local_census_record, document_type: "3", document_number: "#DOCUMENT_NUMBER")
+
+      expect(LocalCensusRecord.count).to eq(5)
+
+      run_rake_task
+
+      expect(LocalCensusRecord.all).to match_array([record1, record2, record3])
+    end
+  end
+end