結合テストで「sign_in」を使用する方法（RSpec）

## 前提内容
・RSpec（Gem）を導入済み
・RSpecの初期ファイルを作成済み

## 実装方法
#### ① rails_helper.rbに記述追加

```ruby:rails_helper.rb
# This file is copied to spec/ when you run 'rails generate rspec:install'
require 'spec_helper'
ENV['RAILS_ENV'] ||= 'test'
require File.expand_path('../config/environment', __dir__)
# Prevent database truncation if the environment is production
abort("The Rails environment is running in production mode!") if Rails.env.production?
require 'rspec/rails'
# Add additional requires below this line. Rails is not loaded until this point!

# Requires supporting ruby files with custom matchers and macros, etc, in
# spec/support/ and its subdirectories. Files matching `spec/**/*_spec.rb` are
# run as spec files by default. This means that files in spec/support that end
# in _spec.rb will both be required and run as specs, causing the specs to be
# run twice. It is recommended that you do not name files matching this glob to
# end with _spec.rb. You can configure this pattern with the --pattern
# option on the command line or in ~/.rspec, .rspec or `.rspec-local`.
#
# The following line is provided for convenience purposes. It has the downside
# of increasing the boot-up time by auto-requiring all files in the support
# directory. Alternatively, in the individual `*_spec.rb` files, manually
# require only the support files necessary.
#
Dir[Rails.root.join('spec', 'support', '**', '*.rb')].sort.each { |f| require f } # ＜　追加　＞

# Checks for pending migrations and applies them before tests are run.
# If you are not using ActiveRecord, you can remove these lines.
begin
  ActiveRecord::Migration.maintain_test_schema!
rescue ActiveRecord::PendingMigrationError => e
  puts e.to_s.strip
  exit 1
end
RSpec.configure do |config|
  config.include SignInSupport # ＜　追加　＞
  # Remove this line if you're not using ActiveRecord or ActiveRecord fixtures
  config.fixture_path = "#{::Rails.root}/spec/fixtures"

  # If you're not using ActiveRecord, or you'd prefer not to run each of your
  # examples within a transaction, remove the following line or assign false
  # instead of true.
  config.use_transactional_fixtures = true

  # You can uncomment this line to turn off ActiveRecord support entirely.
  # config.use_active_record = false

  # RSpec Rails can automatically mix in different behaviours to your tests
  # based on their file location, for example enabling you to call `get` and
  # `post` in specs under `spec/controllers`.
  #
  # You can disable this behaviour by removing the line below, and instead
  # explicitly tag your specs with their type, e.g.:
  #
  #     RSpec.describe UsersController, type: :controller do
  #       # ...
  #     end
  #
  # The different available types are documented in the features, such as in
  # https://relishapp.com/rspec/rspec-rails/docs
  config.infer_spec_type_from_file_location!

  # Filter lines from Rails gems in backtraces.
  config.filter_rails_from_backtrace!
  # arbitrary gems may also be filtered via:
  # config.filter_gems_from_backtrace("gem name")
end
```
　今回追加した記述は23行目の
「Dir[Rails.root.join('spec', 'support', '＊＊', '*.rb')].sort.each { |f| require f }」と28行目の「config.include SignInSupport」です。
　1つの記述はspec/support/配下のファイルを読み込む設定をするためです。
　2つの記述は後ほど作成するspec/support/sign_in_support.rbを読み込むための記述です。

#### ② supportディレクトリを自作する。
#### ③ supportディレクトリ配下にsign_in_support.rbファイルの作成する。

```ruby:sign_in_support.rb
module SignInSupport
  def sign_in(user)
    visit new_user_session_path
    fill_in 'メールアドレス', with: user.email
    fill_in 'パスワード', with: user.password
    find('input[name="commit"]').click
    expect(current_path).to eq tweets_path
  end
end
```

これによりテストコードで「sign_in」を使えるようになる。

```ruby:sign_in_support.rb
require 'rails_helper'

RSpec.describe 'ツイート投稿', type: :system do
  before do
    @user = FactoryBot.create(:user)
    @tweet = FactoryBot.create(:tweet)
  end
  context 'ツイート投稿ができるとき'do
    it 'ログインしたユーザーは新規投稿できる' do
      # ログインする
      sign_in(@user)
    # （省略）
    end
  end
  context 'ツイート投稿ができないとき'do
    it 'ログインしていないとトップページに遷移できない' do
    # （省略）
    end
  end
end
```