Raise a better error when phantomjs returns a non-zero exit status. Fixes #23.

README.md

@@ -196,6 +196,10 @@ makes debugging easier). Running `rake autocompile` will watch the
 
 *   Fix bug where we could end up interacting with an obsolete element. [Issue #30]
 
+*   Raise an suitable error if PhantomJS returns a non-zero exit status.
+    Previously a version error would be raised, indicating that the
+    PhantomJS version was too old when in fact it did not start at all. [Issue #23]
+
 ### 0.4.0 ###
 
 *   Element click position is now calculated using the native

lib/capybara/poltergeist/client.rb

@@ -56,9 +56,13 @@ module Capybara::Poltergeist
       return if @phantomjs_version_checked
 
       version = `#{path} --version`.chomp
-      if version < PHANTOMJS_VERSION
+
+      if $? != 0
+        raise PhantomJSFailed.new($?)
+      elsif version < PHANTOMJS_VERSION
         raise PhantomJSTooOld.new(version)
       end
+
       @phantomjs_version_checked = true
     end
   end

lib/capybara/poltergeist/errors.rb

@@ -82,5 +82,19 @@ module Capybara
         "PhantomJS version #{version} is too old. You must use at least version #{Client::PHANTOMJS_VERSION}"
       end
     end
+
+    class PhantomJSFailed < Error
+      attr_reader :status
+
+      def initialize(status)
+        @status = status
+      end
+
+      def message
+        "PhantomJS returned non-zero exit status #{status.exitstatus}. Ensure there is an X display available and " \
+          "that DISPLAY is set. (See the Poltergeist README for details.) Make sure 'phantomjs --version' " \
+          "runs successfully on your system."
+      end
+    end
   end
 end

spec/unit/client_spec.rb

@@ -17,5 +17,16 @@ module Capybara::Poltergeist
         e.message.should include('1.3.0')
       end
     end
+
+    it 'raises an error if phantomjs returns a non-zero exit code' do
+      subject = Client.new(6000, nil, 'exit 42 && ')
+      expect { subject.start }.to raise_error(Error)
+
+      begin
+        subject.start
+      rescue PhantomJSFailed => e
+        e.message.should include('42')
+      end
+    end
   end
 end