word_filter.rb

class WordFilter
  def initialize(*ng_words)
    @ng_words = ng_words
  end

  def detect(message)
    message =~ /#{@ng_words.join('|')}/
  end

  def censor(message)
    message.gsub(/#{@ng_words.join('|')}/, "<censored>")
  end
end

word_filter_spec.rb

require 'rubygems'
require 'spec'
require 'word_filter'

describe WordFilter do
  it "NGWordをひとつ指定できること" do
    lambda do
      filter = WordFilter.new("NGWord")
    end.should_not raise_error
  end

  it "NGWordを複数指定できること" do
    lambda do
      filter = WordFilter.new("NGWord1", "NGWord2")
    end.should_not raise_error
  end
  
  context "NGWordが指定されている場合" do
    before do
      @filter = WordFilter.new("NGWord")
    end

    it "NGWordをdetectできること" do
      @filter.detect("NGWord").should be_true
    end

    it "NGWordじゃない場合detectしない" do
      @filter.detect("hoge").should be_false
    end

    it "NGWordをcensorできること" do
      @filter.censor("t_wada: あいうNGWord").should == "t_wada: あいう<censored>"
    end

    it "NGWordを含まなければそのまま返すこと" do
      @filter.censor("t_wada: あいうえお").should == "t_wada: あいうえお"
    end
  end

  context "NGWordが複数指定している場合" do
    before do
      @filter = WordFilter.new("NGWord1", "NGWord2")
    end

    it "NGWordをdetectできること" do
      @filter.detect("NGWord1").should be_true
      @filter.detect("NGWord2").should be_true
    end

    it "NGWordをcensorできること" do
      @filter.censor("t_wada: あいうNGWord1").should == "t_wada: あいう<censored>"
      @filter.censor("t_wada: あいうNGWord2").should == "t_wada: あいう<censored>"
      @filter.censor("t_wada: あいうえお").should == "t_wada: あいうえお"
    end
  end

  context "IDがNGWordだったら" do
    before do
      @filter = WordFilter.new('t_wada')
    end

    it "IDはcensorしない" do
      pending
      @filter.censor("t_wada: t_wada").should == "t_wada: <censored>"
    end
  end
end