Gemspecs must not list the same gem as both runtime and development dependency

When you're developing a gem, never list the same dependency as both runtime and development dependency in your .gemspec.

So don't do this:

Copyspec.add_dependency 'activesupport'
spec.add_development_dependency 'activesupport', '~> 2.3'

If you do this, your gemspec will not validate and modern versions of Bundler will silently ignore it. This leads to errors like:

CopyCould not find your-gem-0.1.2 in any of the sources

What to do instead

If you want to freeze a different version of a dependency for your tests, prefer putting it into the Gemfile in your gem project directory.

In the example above, have a .gemspec like this:

Copyspec.add_dependency 'activesupport'

Then, in your Gemfile, add the dependency for tests:

Copygem 'activesupport', '~> 2.3'
gemspec