Find gems that are depending on a given gem

To find the gems that are dependent on a given gem, you can use the following command:

gem dependency eventmachine --reverse-dependencies

Gem eventmachine-1.2.0.1
  rake-compiler (~> 0.9.5, development)
  rake-compiler-dock (~> 0.5.1, development)
  test-unit (~> 2.0, development)
  Used by
    excon-0.51.0 (eventmachine (>= 1.0.4, development))
    thin-1.7.0 (eventmachine (>= 1.0.4, ~> 1.0))

I wanted to find out what is depending on eventmachine in my project. Because, concurrent-ruby is a better alternative to eventmachine. My suspicion was that sucker_punch gem was using it. I was wrong because as you see in the about output, it is not the culprit. The version 2.0 of sucker punch uses concurrent-ruby. Luckily, only the development environment has dependency on the eventmachin gem.