Test and implement CreateComment::CheckProhibitedWords service

app/services/create_comment/check_prohibited_words.rb

@@ -0,0 +1,16 @@
+class CreateComment
+  class CheckProhibitedWords
+    PROHIBITED_WORDS = ['bad', 'cheap', 'boring']
+
+    def self.build
+      new
+    end
+
+    def call(title)
+      count = (title.to_s.split & PROHIBITED_WORDS).size
+      raise ProhibitedWordError if count > 1
+    end
+
+    class ProhibitedWordError < StandardError; end
+  end
+end

spec/services/create_comment/check_prohibited_words_spec.rb

@@ -0,0 +1,19 @@
+require 'rails_helper'
+
+describe CreateComment::CheckProhibitedWords do
+
+  before do
+    @service = CreateComment::CheckProhibitedWords.build
+  end
+
+  it "raises exception if title contains at least two prohibited words" do
+    title = "bad boring movie"
+    expect { @service.call(title) }.
+      to raise_error(CreateComment::CheckProhibitedWords::ProhibitedWordError)
+  end
+
+  it "does not raise if title contains one prohibited word" do
+    title = "cheap but interesting movie"
+    expect { @service.call(title) }.not_to raise_error
+  end
+end