Add a method to finder to find unpublished documents

This method allows the scraper route to send the unpublished
documents to the view so that they can be scraped and pushed to
the static repo, so that they can be loaded as a preview without
being accessible for users or linked from the site

lib/document/finder.rb

@@ -21,11 +21,15 @@ def find_or_empty
     end
 
     def find_all
-      filenames.map { |filename| create_document(filename) }.select(&:published?)
+      create_documents.select(&:published?)
+    end
+
+    def find_previews
+      create_documents.reject(&:published?)
     end
 
     def find_featured
-      find_all.select(&:featured?)
+       create_documents.select(&:featured?)
     end
 
     def multiple?
@@ -49,6 +53,10 @@ def raise_error_if_no_files_found
       raise Document::NoFilesFoundError, message if none?
     end
 
+    def create_documents
+      @create_documents ||= filenames.map { |filename| create_document(filename) }
+    end
+
     def filenames
       @filenames ||= Dir.glob(pattern).sort
     end

tests/document/finder.rb

@@ -33,6 +33,18 @@
     end
   end
 
+  it 'can find unpublished documents' do
+    published = '---
+published: true
+---'
+    unpublished = '---
+published: false
+---'
+    Dir.stub :glob, [new_tempfile(published), new_tempfile(unpublished)] do
+      finder.find_previews.count.must_equal(1)
+    end
+  end
+
   it 'creates a document with the right url' do
     contents = '---
 slug: a-slug