add example of formatter that filters based on options passed to

describe() and it() methods.

examples/passing/filtered_formatter.rb

@@ -0,0 +1,18 @@
+$:.unshift File.join(File.dirname(__FILE__), "/../../lib")
+require 'spec/runner/formatter/nested_text_formatter'
+
+class FilteredFormatter < Spec::Runner::Formatter::NestedTextFormatter
+  def add_example_group(example_group)
+    if example_group.options[:show] == false
+      @showing = false
+    else
+      @showing = true
+      puts example_group.description 
+    end
+  end
+
+  def example_passed(example)
+    puts "  " << example.description if @showing unless example.options[:show] == false
+  end
+end
+

examples/passing/filtered_formatter_example.rb

@@ -0,0 +1,31 @@
+# This demonstrates how you can write custom formatters to handle arbitrary
+# options passed to the +describe+ and +it+ methods. To see it in action, stand
+# in the project root and say:
+# 
+#   bin/spec -r examples/passing/filtered_formatter.rb examples/passing/filtered_formatter_example.rb -f FilteredFormatter
+#   
+# You should only see the examples and groups below that are not explicitly
+# marked :show => false
+#
+#   group 1
+#     example 1 a
+#   group 3
+#     example 3
+
+
+describe "group 1", :show => true do
+  it "example 1 a", :show => true do
+  end
+  it "example 1 b", :show => false do
+  end
+end
+
+describe "group 2", :show => false do
+  it "example 2" do
+  end
+end
+
+describe "group 3" do
+  it "example 3" do
+  end
+end