Make Development::Seeder testable

[louis-antonopoulos]

Following up on 1288: Introduce development:db:seed and development:db:seed:replant tasks, there are a couple small changes that could improve Development::Seeder.load_seeds.

This is where I landed for ReadySetGo:

def self.load_seeds(skip_env_check: false)
  raise(StandardError, "Development::Seeder can only be run in a development environment.") unless skip_env_check || Rails.env.development?

  new.load_seeds
end

Improvements:

1. Development::Seeder becomes testable. You can do things like this:

RSpec.describe(Development::Seeder) do
  describe ".load_seeds" do
    before { Development::Seeder.load_seeds(skip_env_check: true) }

    it "creates exactly one organization" do
      expect(Organization.count).to(eq(1))
      expect(Organization.sole.name).to(eq("thoughtbot"))
    end

    it "is idempotent" do
      Development::Seeder.load_seeds(skip_env_check: true)

      expect(Organization.count).to(eq(1))
   end

2. Rubocop recommends raising some kind of error, not just an open string

3. The early return eliminates the nesting of the conditional with an early return (also a Rubocop thing, but one I love)