gistfile1.txt

$ bundle install
Fetching source index for file:/Users/andre/sw/gems/bundler/tmp/gems/remote2/
Installing rack (1.1.0) 
Installing capybara (0.3.9) 
Installing rails (3.0.0.rc4) 
Using bundler (1.0.4.pre) 
Your bundle is complete! Use `bundle show [gemname]` to see where a bundled gem is installed.



$ cat Gemfile.lock
GEM
  remote: file:/Users/andre/sw/gems/bundler/tmp/gems/remote2/
  specs:
    capybara (0.3.9)
      rack (>= 1.0.0)
    rack (1.1.0)
    rails (3.0.0.rc4)
      rack (~> 1.1.0)

PLATFORMS
  ruby

DEPENDENCIES
  capybara (= 0.3.9)
  rails (= 3.0.0.rc4)

## change requirement to rails, 3.0.0

$ bundle install
Fetching source index for file:/Users/andre/sw/gems/bundler/tmp/gems/remote2/
Bundler could not find compatible versions for gem "rack":
  In snapshot (Gemfile.lock):
    rack (1.1.0)

  In Gemfile:
    rails (= 3.0.0) depends on
      rack (~> 1.2.1)

Running `bundle update` will rebuild your snapshot from scratch, using only
the gems in your Gemfile, which may resolve the conflict.