Implement the cancan filters for diary entries

Access logic is not _entirely_ exported from the controller,
unfortunately.  For interface reasons, some actions which require admin
have to be listed within the controller's deny_access method.

This is required because, being a default-deny system, cancancan
_cannot_ tell you the reason you were denied access; and so
the "nice" feedback presenting next steps can't be gleaned from
the exception

test/models/abilities_test.rb

@@ -4,4 +4,40 @@ require "test_helper"
 
 class AbilityTest < ActiveSupport::TestCase
 
+  test "diary permissions for a guest" do
+    ability = Ability.new(nil, [])
+    [:list, :rss, :view, :comments].each do |action|
+      assert ability.can?(action, DiaryEntry), "should be able to #{action} DiaryEntries"
+    end
+
+    [:create, :edit, :comment, :subscribe, :unsubscribe, :hide, :hidecomment].each do |action|
+      assert ability.cannot?(action, DiaryEntry), "should be able to #{action} DiaryEntries"
+      assert ability.cannot?(action, DiaryComment), "should be able to #{action} DiaryEntries"
+    end
+  end
+
+
+  test "Diary permissions for a normal user" do
+    ability = Ability.new(create(:user), [])
+
+    [:list, :rss, :view, :comments, :create, :edit, :comment, :subscribe, :unsubscribe].each do |action|
+      assert ability.can?(action, DiaryEntry), "should be able to #{action} DiaryEntries"
+    end
+
+    [:hide, :hidecomment].each do |action|
+      assert ability.cannot?(action, DiaryEntry), "should be able to #{action} DiaryEntries"
+      assert ability.cannot?(action, DiaryComment), "should be able to #{action} DiaryEntries"
+    end
+  end
+
+  test "Diary for an administrator" do
+    ability = Ability.new(create(:administrator_user), [])
+    [:list, :rss, :view, :comments, :create, :edit, :comment, :subscribe, :unsubscribe, :hide, :hidecomment].each do |action|
+      assert ability.can?(action, DiaryEntry), "should be able to #{action} DiaryEntries"
+    end
+
+    [:hide, :hidecomment].each do |action|
+      assert ability.can?(action, DiaryComment), "should be able to #{action} DiaryComment"
+    end
+  end
 end