index.html.erb

<div class="container">
  <% if flash[:notice] %>
    <div class="alert alert-success">
      <%= flash[:notice] %>
    </div>
  <% end %>

  <h1>Users</h1>
  <%= form_for(@user_import, url: import_admin_users_path,
    html: {method: :post, multipart: true, role: "form", class: "form-inline"}) do |f| %>
    <% if @user_import.errors.any? %>
      <div class="alert alert-danger">
        <ul>
        <% @user_import.errors.full_messages.each do |msg| %>
          <li><%= msg %></li>
        <% end %>
        </ul>
      </div>
    <% end %>

    <div class="form-group">
      <%= f.file_field :file, class: "form-control" %>
    </div>
    <div class="form-group">
      <%= f.button "Upload", class: ["btn","btn-default"] %>
    </div>
  <% end %>
</div>

user_import.rb

class UserImport
  CSV_OPTIONS = {encoding: 'UTF-8'}.freeze
  include ActiveModel::Model

  attr_accessor :file

  validates :file, presence: true
  validate :csv_format, if: Proc.new { |m| m.file.present? }

  def save
    return false unless valid?

    User.transaction do
      CSV.read(path, "r", CSV_OPTIONS).each_with_index do |row, index|
        user = User.new(email: row[0], first_name: row[1], last_name: row[2])
        unless user.save
          errors.add("line #{index+1} : ", user.errors.full_messages.join(" , "))
        end
      end

      if errors.any?
        raise ActiveRecord::Rollback
      end
    end

    !errors.any?
  end

  private
  def csv_format
    CSV.open(path, "r", CSV_OPTIONS) { |csv| }
  rescue
    errors.add(:file, "is invalid csv format")
  end

  def path
    if file.respond_to? :path
      file.path
    else
      file
    end
  end
end

user_import_spec.rb

require "rails_helper"

RSpec.describe UserImport do
  describe "#file" do
    subject { UserImport.new(file: file) }

    context "設定されていない時" do
      let(:file) { nil }
      it { expect(subject).to have(1).errors_on(:file) }
    end

    context "設定されている時" do
      let(:file) { Rails.root.join("spec/fixtures/valid.csv") }
      it { expect(subject).not_to have(1).errors_on(:file) }
    end

    context "有効なフォーマットの時" do
      let(:file) { Rails.root.join("spec/fixtures/valid.csv") }
      it { expect(subject).not_to have(1).errors_on(:file) }
    end

    context "無効なフォーマットの時" do
      let(:file) { Rails.root.join("spec/fixtures/invalid.csv") }
      it { expect(subject).to have(1).errors_on(:file) }
    end
  end

  describe "#save" do
    subject { UserImport.new(file: file) }
    context "有効なフォーマットの時" do
      let(:file) { Rails.root.join("spec/fixtures/valid.csv") }
      let(:error_count) { CSV.read(file).count }
      it { expect(subject.save).to be_truthy }
      it { expect { subject.save }.to change(User, :count).by(error_count) }
    end

    context "無効なフォーマットの時" do
      let(:file) { Rails.root.join("spec/fixtures/invalid.csv") }
      it { expect(subject.save).to be_falsey }
    end

    context "Userモデルでエラーでがある時" do
      let(:file) { Rails.root.join("spec/fixtures/valid.csv") }
      let(:errors) { double(add: nil, clear: nil, empty?: nil) }
      before do
        allow_any_instance_of(User).to receive(:save) { false }
        expect(subject).to receive(:errors) { errors }.twice
      end
      it { expect(subject.save).to be_falsey }
      it { expect { subject.save }.not_to change(User, :count) }
    end
  end
end

users_controller_spec.rb

require "rails_helper"

RSpec.describe Admin::UsersController do
  describe "GET index" do
    before do
      get :index
    end

    it { expect(assigns(:user_import)).to be_kind_of(UserImport) }
  end

  describe "POST import" do
    let(:attributes) { { file: Rack::Test::UploadedFile.new(file, "text/plan") } }

    describe "with valid params" do
      let(:file) { Rails.root.join("spec/fixtures/valid.csv") }
      let(:record_count) { CSV.read(file).count }

      it "creates new Users" do
        expect {
          post :import, {user_import: attributes}
        }.to change(User, :count).by(record_count)
      end

      it "redirects to the created user" do
        post :import, {user_import: attributes}
        expect(response).to redirect_to(action: :index)
      end
    end

    describe "with invalid params" do
      let(:file) { Rails.root.join("spec/fixtures/invalid.csv") }

      it "do not creates new Users" do
        expect {
          post :import, {user_import: attributes}
        }.not_to change(User, :count)
      end

      it "re-renders the 'index' template" do
        post :import, {user: attributes}
        expect(response).to render_template("index")
      end
    end
  end
end

users_ontroller.rb

class Admin::UsersController < ApplicationController
  def index
    @user_import = UserImport.new
  end

  def import
    @user_import = UserImport.new(params[:user_import])
    if @user_import.save
      redirect_to url_for(action: :index), notice: 'Upload successful'
    else
      render :index
    end
  end
end