Add convenience method to determine whether a user exists

lib/twitter/client/user.rb

@@ -24,6 +24,23 @@ def user(*args)
         format.to_s.downcase == 'xml' ? response['user'] : response
       end
 
+      # Returns true if the specified user exists
+      #
+      # @param user [Integer, String] A Twitter user ID or screen name.
+      # @return [Boolean] true if the user exists, otherwise false.
+      # @example Return true if @sferik exists
+      #     Twitter.user?("sferik")
+      #     Twitter.user?(7505382)  # Same as above
+      # @authenticated false
+      # @rate_limited true
+      def user?(user, options={})
+        merge_user_into_options!(user, options)
+        get('users/show', options, true)
+        true
+      rescue Twitter::NotFound
+        false
+      end
+
       # Returns extended information for up to 100 users
       #
       # @format :json, :xml

spec/twitter/client/user_spec.rb

@@ -102,6 +102,36 @@
 
       end
 
+      describe ".user?" do
+
+        before do
+          stub_get("users/show.#{format}").
+            with(:query => {:screen_name => "sferik"}).
+            to_return(:body => fixture("sferik.#{format}"), :headers => {:content_type => "application/#{format}; charset=utf-8"})
+          stub_get("users/show.#{format}").
+            with(:query => {:screen_name => "pengwynn"}).
+            to_return(:body => fixture("not_found.#{format}"), :status => 404, :headers => {:content_type => "application/#{format}; charset=utf-8"})
+        end
+
+        it "should get the correct resource" do
+          @client.user?("sferik")
+          a_get("users/show.#{format}").
+            with(:query => {:screen_name => "sferik"}).
+            should have_been_made
+        end
+
+        it "should return true if user exists" do
+          user = @client.user?("sferik")
+          user.should be_true
+        end
+
+        it "should return false if user does not exists" do
+          user = @client.user?("pengwynn")
+          user.should be_false
+        end
+
+      end
+
       describe ".users" do
 
         context "with screen names passed" do