add tests for expected layout of files in repo

References: Homebrew#4914

test/layout_test.rb

@@ -0,0 +1,77 @@
+require 'test_helper'
+
+describe "Repo layout" do
+  project_root = Pathname.new(File.expand_path("#{File.dirname(__FILE__)}/../"))
+
+  # todo: a more clever way to do this would be to dispense with
+  #       the imperfect IGNORE lists and read the actual repo
+  #       contents by running "git ls-files
+
+  # dot dirs are always a project of Dir.entries
+  # other files are items that the developer hopefully has gitignored
+  IGNORE_FILES = %w{
+                    .
+                    ..
+                    .DS_Store
+                   }
+
+  # the developer has hopefully gitignored these
+  IGNORE_REGEXPS = [
+                    %r{~$},      # emacs
+                   ]
+
+  TOPLEVEL_DIRS = %w{
+                     .git
+                     Casks
+                     bin
+                     developer
+                     doc
+                     lib
+                     test
+                    }
+
+  TOPLEVEL_FILES = %w{
+                      .gitignore
+                      .travis.yml
+                      CONDUCT.md
+                      CONTRIBUTING.md
+                      Gemfile
+                      Gemfile.lock
+                      LICENSE
+                      README.md
+                      Rakefile
+                      USAGE.md
+                      brew-cask.rb
+                     }
+
+  describe "toplevel dir" do
+    it "finds some files at the top level" do
+      entries = Dir.entries(project_root)
+      entries.length.must_be :>, 0
+    end
+
+    it "only finds expected files at the top level" do
+      entries = Dir.entries(project_root) - IGNORE_FILES - TOPLEVEL_DIRS - TOPLEVEL_FILES
+      IGNORE_REGEXPS.each do |regexp|
+        entries.reject! { |elt| elt.match(regexp) }
+      end
+      entries.length.must_be :==, 0
+    end
+  end
+
+  describe "Casks dir" do
+    it "finds some files in the Casks dir" do
+      entries = Dir.entries(project_root.join('Casks'))
+      entries.length.must_be :>, 0
+    end
+
+    it "only finds .rb files in the Casks dir" do
+      entries = Dir.entries(project_root.join('Casks')) - IGNORE_FILES
+      IGNORE_REGEXPS.each do |regexp|
+        entries.reject! { |elt| elt.match(regexp) }
+      end
+      entries.reject! { |elt| elt.match(%r{\.rb$}) }
+      entries.length.must_be :==, 0
+    end
+  end
+end