Add abstract Repository class

The default behaviour is to raise an exception if set or get methods are
not defined in the repository.

lib/flop.rb

@@ -1,6 +1,8 @@
 require 'flop/version'
 
 require 'flop/feature'
+
+require 'flop/repository'
 require 'flop/repository/memory'
 require 'flop/repository/redis'
 

lib/flop/repository.rb

@@ -0,0 +1,14 @@
+module Flop
+  class Repository
+    def get(name)
+      raise GetNotImplemented
+    end
+
+    def set(name, value)
+      raise SetNotImplemented
+    end
+
+    GetNotImplemented = Class.new(StandardError)
+    SetNotImplemented = Class.new(StandardError)
+  end
+end

lib/flop/repository/memory.rb

@@ -1,6 +1,6 @@
 module Flop
-  module Repository
-    class Memory
+  class Repository
+    class Memory < Flop::Repository
       def initialize
         @features = Hash.new(false)
       end

lib/flop/repository/redis.rb

@@ -1,6 +1,6 @@
 module Flop
-  module Repository
-    class Redis
+  class Repository
+    class Redis < Flop::Repository
       def initialize(redis, namespace = '')
         @redis = redis
         @namespace = namespace

test/flop/repository_test.rb

@@ -0,0 +1,19 @@
+require 'test_helper'
+
+class Flop::RepositoryTest < Minitest::Test
+  def setup
+    @repo = Flop::Repository.new
+  end
+
+  def test_get_raises_exception
+    assert_raises(Flop::Repository::GetNotImplemented) do
+      @repo.get(:test)
+    end
+  end
+
+  def test_set_raises_exception
+    assert_raises(Flop::Repository::SetNotImplemented) do
+      @repo.set(:test, true)
+    end
+  end
+end