Basic tests for a mounted application

This sets up a barebones mounted Rails engine so that tests can be
performed against it.

This follows a similar approach to the other rake tasks test and thus
doesn't intend to be too exhaustive in what is testing and is mostly a
cursory test that one of the tasks does perform differently in a mounted
Rails engine context.

.gitignore

@@ -1,5 +1,6 @@
 /.bundle
 /pkg
+/test/mounted_app/test/dummy/log
 /test/test_app/log
 node_modules
 .byebug_history

test/engine_rake_tasks_test.rb

@@ -0,0 +1,39 @@
+require "test_helper"
+
+class EngineRakeTasksTest < Minitest::Test
+  def setup
+    remove_webpack_binstubs
+  end
+
+  def teardown
+    remove_webpack_binstubs
+  end
+
+  def test_task_mounted
+    output = Dir.chdir(mounted_app_path) { `rake -T` }
+    assert_includes output, "app:webpacker"
+  end
+
+  def test_binstubs
+    Dir.chdir(mounted_app_path) { `bundle exec rake app:webpacker:binstubs` }
+    webpack_binstub_paths.each { |path| assert File.exist?(path) }
+  end
+
+  private
+    def mounted_app_path
+      File.expand_path("mounted_app", __dir__)
+    end
+
+    def webpack_binstub_paths
+      [
+        "#{mounted_app_path}/test/dummy/bin/webpack",
+        "#{mounted_app_path}/test/dummy/bin/webpack-dev-server",
+      ]
+    end
+
+    def remove_webpack_binstubs
+      webpack_binstub_paths.each do |path|
+        File.delete(path) if File.exist?(path)
+      end
+    end
+end

test/mounted_app/Rakefile

@@ -0,0 +1,4 @@
+require "bundler/setup"
+
+APP_RAKEFILE = File.expand_path("test/dummy/Rakefile", __dir__)
+load "rails/tasks/engine.rake"

test/mounted_app/test/dummy/Rakefile

@@ -0,0 +1,3 @@
+require_relative "config/application"
+
+Rails.application.load_tasks

test/mounted_app/test/dummy/bin/rails

@@ -0,0 +1,3 @@
+#!/usr/bin/env ruby
+APP_PATH = File.expand_path("../config/application", __dir__)
+require "rails/commands"

test/mounted_app/test/dummy/bin/rake

@@ -0,0 +1,3 @@
+#!/usr/bin/env ruby
+require "rake"
+Rake.application.run

test/mounted_app/test/dummy/config.ru

@@ -0,0 +1,5 @@
+# This file allows the `Rails.root` to be correctly determined.
+
+require_relative "config/environment"
+
+run Rails.application

test/mounted_app/test/dummy/config/application.rb

@@ -0,0 +1,10 @@
+require "action_controller/railtie"
+require "action_view/railtie"
+require "webpacker"
+
+module TestDummyApp
+  class Application < Rails::Application
+    config.secret_key_base = "abcdef"
+    config.eager_load = true
+  end
+end

test/mounted_app/test/dummy/config/environment.rb

@@ -0,0 +1,3 @@
+require_relative "application"
+
+Rails.application.initialize!

test/mounted_app/test/dummy/config/webpacker.yml

@@ -0,0 +1,75 @@
+# Note: You must restart bin/webpack-dev-server for changes to take effect
+
+default: &default
+  source_path: app/javascript
+  source_entry_path: packs
+  public_output_path: packs
+  cache_path: tmp/cache/webpacker
+
+  # Additional paths webpack should lookup modules
+  # ['app/assets', 'engine/foo/app/assets']
+  resolved_paths:
+    - app/assets
+    - /etc/yarn
+
+  # Reload manifest.json on all requests so we reload latest compiled packs
+  cache_manifest: false
+
+  extensions:
+    - .js
+    - .sass
+    - .scss
+    - .css
+    - .module.sass
+    - .module.scss
+    - .module.css
+    - .png
+    - .svg
+    - .gif
+    - .jpeg
+    - .jpg
+
+development:
+  <<: *default
+  compile: true
+
+  # Reference: https://webpack.js.org/configuration/dev-server/
+  dev_server:
+    https: false
+    host: localhost
+    port: 3035
+    public: localhost:3035
+    hmr: false
+    # Inline should be set to true if using HMR
+    inline: true
+    overlay: true
+    disable_host_check: true
+    use_local_ip: false
+
+test:
+  <<: *default
+  compile: true
+
+  # Compile test packs to a separate directory
+  public_output_path: packs-test
+
+production:
+  <<: *default
+
+  # Production depends on precompilation of packs prior to booting for performance.
+  compile: false
+
+  # Cache manifest.json for performance
+  cache_manifest: true
+
+staging:
+  <<: *default
+
+  # Production depends on precompilation of packs prior to booting for performance.
+  compile: false
+
+  # Cache manifest.json for performance
+  cache_manifest: true
+
+  # Compile staging packs to a separate directory
+  public_output_path: packs-staging

test/mounted_app/test/dummy/package.json

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+{
+  "private": true,
+  "dependencies": {
+    "@rails/webpacker": "file:../../../../"
+  },
+  "license": "MIT"
+}