Add EmberCli::PathSet characterization tests

`PathSet` involves the filesystem, but was previously implemented with
`Rails.root`.

This commit add configuration arguments to the `PathSet` constructor.

Adds test coverage using `tmp` directories.

lib/ember-cli-rails.rb

@@ -1,6 +1,8 @@
 require "ember-cli/engine" if defined?(Rails)
 
 module EmberCli
+  class DependencyError < StandardError; end
+
   extend self
 
   autoload :App,           "ember-cli/app"

lib/ember-cli/app.rb

@@ -15,7 +15,13 @@ class BuildError < StandardError; end
 
     def initialize(name, **options)
       @name, @options = name.to_s, options
-      @paths = PathSet.new(self)
+      @paths = PathSet.new(
+        app: self,
+        configuration: EmberCli.configuration,
+        environment: Rails.env,
+        rails_root: Rails.root,
+        ember_cli_root: EmberCli.root,
+      )
     end
 
     def compile

lib/ember-cli/path_set.rb

@@ -11,34 +11,42 @@ def self.define_path(name, &definition)
       end
     end
 
-    def initialize(app)
+    def initialize(app:, rails_root:, ember_cli_root:, environment:, configuration:)
       @app = app
+      @configuration = configuration
+      @rails_root = rails_root
+      @environment = environment
+      @ember_cli_root = ember_cli_root
     end
 
     define_path :root do
       path = app_options.fetch(:path){ default_root }
       pathname = Pathname.new(path)
-      pathname.absolute?? pathname : Rails.root.join(path)
+      if pathname.absolute?
+        pathname
+      else
+        rails_root.join(path)
+      end
     end
 
     define_path :tmp do
       root.join("tmp").tap(&:mkpath)
     end
 
     define_path :log do
-      Rails.root.join("log", "ember-#{app_name}.#{Rails.env}.log")
+      rails_root.join("log", "ember-#{app_name}.#{environment}.log")
     end
 
     define_path :dist do
-      EmberCli.root.join("apps", app_name).tap(&:mkpath)
+      ember_cli_root.join("apps", app_name).tap(&:mkpath)
     end
 
     define_path :assets do
-      EmberCli.root.join("assets").tap(&:mkpath)
+      ember_cli_root.join("assets").tap(&:mkpath)
     end
 
     define_path :applications do
-      Rails.root.join("public", "_apps").tap(&:mkpath)
+      rails_root.join("public", "_apps").tap(&:mkpath)
     end
 
     define_path :gemfile do
@@ -49,20 +57,26 @@ def initialize(app)
       dist.join("tests")
     end
 
+    define_path :node_modules do
+      root.join("node_modules")
+    end
+
     define_path :package_json_file do
       root.join("package.json")
     end
 
-    define_path :node_modules do
-      root.join("node_modules")
+    define_path :addon_package_json_file do
+      node_modules.join("ember-cli-rails-addon", "package.json")
     end
 
     define_path :ember do
       root.join("node_modules", ".bin", "ember").tap do |path|
-        fail <<-MSG.strip_heredoc unless path.executable?
-          No local ember executable found. You should run `npm install`
-          inside the #{app_name} app located at #{root}
-        MSG
+        unless path.executable?
+          fail DependencyError.new <<-MSG.strip_heredoc
+            No local ember executable found. You should run `npm install`
+            inside the #{app_name} app located at #{root}
+          MSG
+        end
       end
     end
 
@@ -75,34 +89,29 @@ def initialize(app)
     end
 
     define_path :tee do
-      app_options.fetch(:tee_path){ configuration.tee_path }
+      app_options.fetch(:tee_path) { configuration.tee_path }
     end
 
     define_path :bower do
       app_options.fetch(:bower_path) { configuration.bower_path }
     end
 
     define_path :npm do
-      app_options.fetch(:npm_path){ configuration.npm_path }
+      app_options.fetch(:npm_path) { configuration.npm_path }
     end
 
     define_path :bundler do
-      app_options.fetch(:bundler_path){ configuration.bundler_path }
-    end
-
-    define_path :addon_package_json_file do
-      root.join("node_modules", "ember-cli-rails-addon", "package.json")
+      app_options.fetch(:bundler_path) { configuration.bundler_path }
     end
 
     private
 
-    attr_reader :app
+    attr_reader :app, :configuration, :ember_cli_root, :environment, :rails_root
 
     delegate :name, :options, to: :app, prefix: true
-    delegate :configuration, to: EmberCli
 
     def default_root
-      Rails.root.join(app_name)
+      rails_root.join(app_name)
     end
   end
 end