Add matcher for javascript error checking

lib/capybara/webkit/matchers.rb

@@ -0,0 +1,39 @@
+module Capybara
+  module Webkit
+    module RspecMatchers
+      extend RSpec::Matchers::DSL
+
+      matcher :have_errors do |expected|
+        match do |actual|
+          actual = resolve(actual)
+          actual.error_messages.any?
+        end
+
+        failure_message_for_should do |actual|
+          "Expected Javascript errors, but there were none."
+        end
+        failure_message_for_should_not do |actual|
+          actual = resolve(actual)
+          "Expected no Javascript errors, got:\n#{error_messages_for(actual)}"
+        end
+
+        def error_messages_for(obj)
+          obj.error_messages.map do |m|
+            "  - #{m[:message]}"
+          end.join("\n")
+        end
+
+        def resolve(actual)
+          if actual.respond_to? :page
+            actual.page.driver
+          elsif actual.respond_to? :driver
+            actual.driver
+          else
+            actual
+          end
+        end
+      end
+
+    end
+  end
+end