Railsの Fixtureの YAMLには Rubyのコードもかけるらしい

Class: Fixtures

Some times you don‘t care about the content of the fixtures as much as you care about the volume. In these cases, you can mix ERb in with your YAML or CSV fixtures to create a bunch of fixtures for load testing, like:

<% for i in 1..1000 %>
fix_<%= i %>:
id: <%= i %>
name: guy_<%= 1 %>
<% end %>

これは使えるかも