database_cleaner.rb

RSpec.configure do |config|
  config.use_transactional_fixtures = false

  config.before(:suite) do
    DatabaseCleaner.strategy = :transaction
    DatabaseCleaner.clean_with(:truncation)
  end

  config.around(:each) do |example|
    DatabaseCleaner.cleaning do
      example.run
    end
  end
end

report_spec.rb

require "rails_helper"

RSpec.describe ReportMailer, type: :mailer do
  describe "send_daily_report_to" do
    before :all do
      @subscriber = build(:subscriber)
      @mail = ReportMailer.send_daily_report_to @subscriber
      @leads = create_list(:lead, 3) 
    end

    context "there are 3 leads in the system" do
      it "renders the headers" do
        expect(mail.subject).to eq(I18n.t('daily_report_subject'))
        expect(mail.to).to eq([@subscriber.email])
        expect(mail.from).to eq(["[email protected]"])
      end

      it "renders the body with 3 leads" do
        byebug
        expect(mail.body.encoded).to match("Hi")
      end
    end
  end
end