Raised by Resolver when a dependency requests a gem for which there is no spec.
The unsatisfiable dependency. This is a Gem::Resolver::DependencyRequest, not a Gem::Dependency
Creates a new UnsatisfiableDependencyError
for the unsatisfiable Gem::Resolver::DependencyRequest
dep
 
               # File rubygems/exceptions.rb, line 257
def initialize(dep, platform_mismatch=nil)
  if platform_mismatch and !platform_mismatch.empty?
    plats = platform_mismatch.map { |x| x.platform.to_s }.sort.uniq
    super "Unable to resolve dependency: No match for '#{dep}' on this platform. Found: #{plats.join(', ')}"
  else
    if dep.explicit?
      super "Unable to resolve dependency: user requested '#{dep}'"
    else
      super "Unable to resolve dependency: '#{dep.request_context}' requires '#{dep}'"
    end
  end
  @dependency = dep
  @errors     = []
end