Setup Guard

Adds a generic Guardfile.

`spec_helper.rb` includes a stub on `Setting` in a before(:each), which
prevents various spec files from running without the rest of the
suite. This pattern also has the issue that it stubs
`Setting#cache_backend` without warning to developers, giving unexpected
results. We should find a way to remove it. See #38.

In the meanwhile, we introduce a guard to prevent errors, and allow
modules that don't depend on `Setting` to be tested independently.

Gemfile

@@ -57,6 +57,7 @@ group :development, :test do
 end
 
 group :development do
+  gem 'guard-rspec'
   # Access an IRB console on exception pages or by using <%= console %> in views
   gem 'web-console', '~> 2.0'
 end

Guardfile

@@ -0,0 +1,30 @@
+# A sample Guardfile
+# More info at https://github.com/guard/guard#readme
+
+## Uncomment and set this to only include directories you want to watch
+# directories %w(app lib config test spec features) \
+#  .select{|d| Dir.exists?(d) ? d : UI.warning("Directory #{d} does not exist")}
+
+## Note: if you are using the `directories` clause above and you are not
+## watching the project directory ('.'), then you will want to move
+## the Guardfile to a watched dir and symlink it back, e.g.
+#
+#  $ mkdir config
+#  $ mv Guardfile config/
+#  $ ln -s config/Guardfile .
+#
+# and, you'll have to watch "config/Guardfile" instead of "Guardfile"
+
+# Using -W0 to suppress warnings in automatic test runs
+guard :rspec, cmd: 'RUBYOPT="-W0" bundle exec rspec' do
+  require 'guard/rspec/dsl'
+  dsl = Guard::RSpec::Dsl.new(self)
+
+  # Feel free to open issues for suggestions and improvements
+
+  # RSpec files
+  rspec = dsl.rspec
+  watch(rspec.spec_helper)  { rspec.spec_dir }
+  watch(rspec.spec_support) { rspec.spec_dir }
+  watch(rspec.spec_files)
+end

spec/spec_helper.rb

@@ -45,7 +45,10 @@
   end
 
   config.before(:each) do
-    allow(Setting).to receive(:cache_backend).and_return('repository')
+    # @todo: Eliminate this.
+    if Object.const_defined?('Setting')
+      allow(Setting).to receive(:cache_backend).and_return('repository')
+    end
   end
 
 # The settings below are suggested to provide a good initial experience