Implement Rubygem::install

Use the code of `gem-install` command as a basis.

Signed-off-by: Kyrylo Silin <kyrylosilin@gmail.com>

lib/pry/commands/gem_install.rb

@@ -16,19 +16,9 @@ class Pry
     end
 
     def process(gem)
-      begin
-        destination = File.writable?(Gem.dir) ? Gem.dir : Gem.user_dir
-        installer = Gem::DependencyInstaller.new :install_dir => destination
-        installer.install gem
-      rescue Errno::EACCES
-        raise CommandError, "Insufficient permissions to install `#{text.green gem}`."
-      rescue Gem::GemNotFoundException
-        raise CommandError, "Gem `#{text.green gem}` not found."
-      else
-        Gem.refresh
-        output.puts "Gem `#{text.green gem}` installed."
-        require gem
-      end
+      Rubygem.install(gem)
+      output.puts "Gem `#{ text.green(gem) }` installed."
+      require gem
     end
   end
 

lib/pry/rubygem.rb

@@ -1,9 +1,10 @@
+require 'rubygems'
+
 class Pry
   module Rubygem
 
     class << self
       def installed?(name)
-        require 'rubygems'
         if Gem::Specification.respond_to?(:find_all_by_name)
           Gem::Specification.find_all_by_name(name).any?
         else
@@ -50,6 +51,23 @@ class Pry
           self.list.map(&:name)
         end
       end
+
+      # Installs a gem with all its dependencies.
+      #
+      # @param [String] name
+      # @return [void]
+      def install(name)
+        destination = File.writable?(Gem.dir) ? Gem.dir : Gem.user_dir
+        installer = Gem::DependencyInstaller.new(:install_dir => destination)
+        installer.install(name)
+      rescue Errno::EACCES
+        raise CommandError,
+          "Insufficient permissions to install `#{ text.green(name) }`."
+      rescue Gem::GemNotFoundException
+        raise CommandError, "Gem `#{ text.green(name) }` not found."
+      else
+        Gem.refresh
+      end
     end
 
   end