diff --git a/Gemfile b/Gemfile
index 1f00b8752..532cca3f4 100644
--- a/Gemfile
+++ b/Gemfile
@@ -9,3 +9,13 @@ gem "rubocop", ">= 0.47", require: false
 group :test do
   gem "minitest", "~> 5.0"
 end
+
+if ENV["USE_PRY"]
+  gem "awesome_print"
+  gem "pry"
+  gem "pry-byebug"
+  gem "pry-doc"
+  gem "pry-rails"
+  gem "pry-rescue"
+  gem "pry-stack_explorer"
+end
diff --git a/Gemfile.lock b/Gemfile.lock
index fb75154fa..f49deed5b 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -48,12 +48,19 @@ GEM
       tzinfo (~> 1.1)
     arel (7.1.4)
     ast (2.3.0)
+    awesome_print (1.8.0)
+    binding_of_caller (0.7.2)
+      debug_inspector (>= 0.0.1)
     builder (3.2.3)
+    byebug (9.0.6)
+    coderay (1.1.1)
     concurrent-ruby (1.0.5)
+    debug_inspector (0.0.3)
     erubis (2.7.0)
     globalid (0.3.7)
       activesupport (>= 4.1.0)
     i18n (0.8.1)
+    interception (0.5)
     loofah (2.0.3)
       nokogiri (>= 1.5.9)
     mail (2.6.4)
@@ -71,6 +78,24 @@ GEM
     parser (2.4.0.0)
       ast (~> 2.2)
     powerpack (0.1.1)
+    pry (0.10.4)
+      coderay (~> 1.1.0)
+      method_source (~> 0.8.1)
+      slop (~> 3.4)
+    pry-byebug (3.4.2)
+      byebug (~> 9.0)
+      pry (~> 0.10)
+    pry-doc (0.10.0)
+      pry (~> 0.9)
+      yard (~> 0.9)
+    pry-rails (0.3.6)
+      pry (>= 0.10.4)
+    pry-rescue (1.4.5)
+      interception (>= 0.5)
+      pry
+    pry-stack_explorer (0.4.9.2)
+      binding_of_caller (>= 0.7)
+      pry (>= 0.9.11)
     rack (2.0.1)
     rack-test (0.6.3)
       rack (>= 1.0)
@@ -106,6 +131,7 @@ GEM
       ruby-progressbar (~> 1.7)
       unicode-display_width (~> 1.0, >= 1.0.1)
     ruby-progressbar (1.8.1)
+    slop (3.6.0)
     sprockets (3.7.1)
       concurrent-ruby (~> 1.0)
       rack (> 1, < 3)
@@ -121,17 +147,25 @@ GEM
     websocket-driver (0.6.5)
       websocket-extensions (>= 0.1.0)
     websocket-extensions (0.1.2)
+    yard (0.9.9)
 
 PLATFORMS
   ruby
 
 DEPENDENCIES
+  awesome_print
   bundler (~> 1.12)
   minitest (~> 5.0)
+  pry
+  pry-byebug
+  pry-doc
+  pry-rails
+  pry-rescue
+  pry-stack_explorer
   rails
   rake (>= 11.1)
   rubocop (>= 0.47)
   webpacker!
 
 BUNDLED WITH
-   1.14.6
+   1.15.3
diff --git a/README.md b/README.md
index 60c079ff6..2433bd2fd 100644
--- a/README.md
+++ b/README.md
@@ -367,8 +367,14 @@ development:
     host: 0.0.0.0
     port: 8080
     https: false
+    hot: false
 ```
 
+If you have hot turned to `true`, then the `stylesheet_pack_tag` generates no output, as you will want
+to configure your styles to be inlined in your JavaScript for hot reloading. During production and testing, the
+`stylesheet_pack_tag` will create the appropriate HTML tags.
+
+
 #### Resolved Paths
 
 If you are adding webpacker to an existing app that has most of the assets inside
@@ -601,8 +607,12 @@ and
 
 #### React
 
-You may consider using [react-rails](https://github.com/reactjs/react-rails) or
-[webpacker-react](https://github.com/renchap/webpacker-react) for more advanced react integration. However here is how you can do it yourself:
+The most widely used React integration is [shakacode/react_on_rails](https://github.com/shakacode/react_on_rails) which includes support for server rendering, redux and react-router.
+
+Other alternatives include [react-rails](https://github.com/reactjs/react-rails) and 
+[webpacker-react](https://github.com/renchap/webpacker-react) for more advanced react integration. 
+
+If you're not concerned with view helpers to pass props or server rendering, can do it yourself:
 
 ```erb
 <%# views/layouts/application.html.erb %>
@@ -1103,6 +1113,8 @@ git push heroku master
 Webpacker lazily compiles assets in test env so you can write your tests without any extra
 setup and everything will just work out of the box.
 
+Note, [React on Rails] users should set configuration value `compile` to false, as React on Rails
+handle compilation for test and production environments.
 
 Here is a sample system test case with hello_react example component:
 
diff --git a/lib/install/config/webpack/shared.js b/lib/install/config/webpack/shared.js
index 45abc33b6..8b25115df 100644
--- a/lib/install/config/webpack/shared.js
+++ b/lib/install/config/webpack/shared.js
@@ -28,7 +28,6 @@ module.exports = {
   output: {
     filename: '[name].js',
     path: output.path,
-    publicPath: output.publicPath
   },
 
   module: {
@@ -39,7 +38,6 @@ module.exports = {
     new webpack.EnvironmentPlugin(JSON.parse(JSON.stringify(env))),
     new ExtractTextPlugin(env.NODE_ENV === 'production' ? '[name]-[hash].css' : '[name].css'),
     new ManifestPlugin({
-      publicPath: output.publicPath,
       writeToFileEmit: true
     })
   ],
diff --git a/lib/install/config/webpacker.yml b/lib/install/config/webpacker.yml
index b670ae4cd..15df260f7 100644
--- a/lib/install/config/webpacker.yml
+++ b/lib/install/config/webpacker.yml
@@ -34,6 +34,7 @@ development:
     host: localhost
     port: 8080
     https: false
+    hot: false
 
 test:
   <<: *default
diff --git a/lib/webpacker.rb b/lib/webpacker.rb
index 2a2791634..db55fe0bf 100644
--- a/lib/webpacker.rb
+++ b/lib/webpacker.rb
@@ -2,14 +2,15 @@ module Webpacker
   extend self
 
   def bootstrap
-    Webpacker::Env.load
-    Webpacker::Configuration.load
-    Webpacker::Manifest.load
+    Webpacker::Env.load_instance
+    Webpacker::Configuration.load_instance
+    Webpacker::DevServer.load_instance
+    Webpacker::Manifest.load_instance
   end
 
   def compile
     Webpacker::Compiler.compile
-    Webpacker::Manifest.load
+    Webpacker::Manifest.load_instance
   end
 
   def env
@@ -19,6 +20,7 @@ def env
 
 require "webpacker/env"
 require "webpacker/configuration"
+require "webpacker/dev_server"
 require "webpacker/manifest"
 require "webpacker/compiler"
 require "webpacker/railtie" if defined?(Rails)
diff --git a/lib/webpacker/configuration.rb b/lib/webpacker/configuration.rb
index b20808d9e..edd5e102a 100644
--- a/lib/webpacker/configuration.rb
+++ b/lib/webpacker/configuration.rb
@@ -4,12 +4,21 @@
 
 class Webpacker::Configuration < Webpacker::FileLoader
   class << self
+    def reset
+      @defaults = nil
+      super
+    end
+
     def entry_path
       source_path.join(fetch(:source_entry_path))
     end
 
+    def public_output_path
+      fetch(:public_output_path)
+    end
+
     def output_path
-      public_path.join(fetch(:public_output_path))
+      public_path.join(public_output_path)
     end
 
     def manifest_path
@@ -45,19 +54,30 @@ def fetch(key)
     end
 
     def data
-      load if Webpacker.env.development?
-      raise Webpacker::FileLoader::FileLoaderError.new("Webpacker::Configuration.load must be called first") unless instance
+      load_instance if Webpacker.env.development?
+      raise Webpacker::FileLoader::FileLoaderError.new("Webpacker::Configuration.load_data must be called first") unless instance
       instance.data
     end
 
     def defaults
       @defaults ||= HashWithIndifferentAccess.new(YAML.load(default_file_path.read)[Webpacker.env])
     end
+
+    # Uses the webpack dev server host if appropriate
+    def output_path_or_url
+      if Webpacker::DevServer.dev_server?
+        Webpacker::DevServer.base_url
+      else
+        # Ensure we start with a slash so that the asset helpers don't prepend the default asset
+        # pipeline locations.
+        public_output_path.starts_with?("/") ? public_output_path : "/#{public_output_path}"
+      end
+    end
   end
 
   private
-    def load
-      return super unless File.exist?(@path)
+    def load_data
+      return Webpacker::Configuration.defaults unless File.exist?(@path)
       HashWithIndifferentAccess.new(YAML.load(File.read(@path))[Webpacker.env])
     end
 end
diff --git a/lib/webpacker/dev_server.rb b/lib/webpacker/dev_server.rb
new file mode 100644
index 000000000..ceb931026
--- /dev/null
+++ b/lib/webpacker/dev_server.rb
@@ -0,0 +1,78 @@
+# Same convention as manifest/configuration.rb
+
+# Loads webpacker configuration from config/webpacker.yml
+
+require "webpacker/configuration"
+
+class Webpacker::DevServer < Webpacker::FileLoader
+  class << self
+    def dev_server?
+      !dev_server_values.nil?
+    end
+
+    # read settings for dev_server
+    def hot?
+      return false unless dev_server?
+      if ENV["WEBPACKER_HMR"].present?
+        val = ENV["WEBPACKER_HMR"].downcase
+        return true if val == "true"
+        return false if val == "false"
+        raise new ArgumentError("WEBPACKER_HMR value is #{ENV['WEBPACKER_HMR']}. Set to TRUE|FALSE")
+      end
+      fetch(:hot)
+    end
+
+    def host
+      fetch(:host)
+    end
+
+    def port
+      fetch(:port)
+    end
+
+    def https?
+      fetch(:https)
+    end
+
+    def protocol
+      https? ? "https" : "http"
+    end
+
+    def file_path
+      Webpacker::Configuration.file_path
+    end
+
+    # Uses the hot_reloading_host if appropriate
+    def base_url
+      "#{protocol}://#{host}:#{port}"
+    end
+
+    private
+
+    def dev_server_values
+      data.fetch(:dev_server, nil)
+    end
+
+    def fetch(key)
+      return nil unless dev_server?
+      dev_server_values.fetch(key, dev_server_defaults[key])
+    end
+
+    def data
+      load_instance if Webpacker.env.development?
+      unless instance
+        raise Webpacker::FileLoader::FileLoaderError.new("Webpacker::DevServer.load_data must be called first")
+      end
+      instance.data
+    end
+
+    def dev_server_defaults
+      @defaults ||= Webpacker::Configuration.defaults[:dev_server]
+    end
+  end
+
+  private
+    def load_data
+      Webpacker::Configuration.instance.data
+    end
+end
diff --git a/lib/webpacker/env.rb b/lib/webpacker/env.rb
index f7a385e37..1f276e3bb 100644
--- a/lib/webpacker/env.rb
+++ b/lib/webpacker/env.rb
@@ -14,7 +14,7 @@ def file_path
   end
 
   private
-    def load
+    def load_data
       environments = File.exist?(@path) ? YAML.load(File.read(@path)).keys : [].freeze
       return ENV["NODE_ENV"] if environments.include?(ENV["NODE_ENV"])
       return Rails.env if environments.include?(Rails.env)
diff --git a/lib/webpacker/file_loader.rb b/lib/webpacker/file_loader.rb
index 8d478420b..ea01f7016 100644
--- a/lib/webpacker/file_loader.rb
+++ b/lib/webpacker/file_loader.rb
@@ -4,21 +4,44 @@ class NotFoundError < StandardError; end
   class FileLoaderError < StandardError; end
 
   class_attribute :instance
-  attr_accessor :data
+  attr_accessor :data, :mtime, :path
 
   class << self
-    def load(path = file_path)
+    def load_instance(path = file_path)
+      # Assume production is 100% cached and don't reload if file's mtime not changed
+      cached = self.instance && # if we have a singleton
+        (env == "production" || # skip if production bc always cached
+          (File.exist?(path) && self.instance.mtime == File.mtime(path))) # skip if mtime not changed
+
+      return if cached
       self.instance = new(path)
     end
+
+    def file_path
+      raise FileLoaderError.new("Subclass of Webpacker::FileLoader should override this method")
+    end
+
+    def reset
+      self.instance = nil
+      load_instance
+    end
+
+    private
+
+    # Prefer the NODE_ENV to the rails env.
+    def env
+      ENV["NODE_ENV"].presence || Rails.env
+    end
   end
 
   private
     def initialize(path)
       @path = path
-      @data = load
+      @mtime = File.exist?(path) ? File.mtime(path) : nil
+      @data = load_data
     end
 
-    def load
+    def load_data
       {}.freeze
     end
 end
diff --git a/lib/webpacker/helper.rb b/lib/webpacker/helper.rb
index e90997e41..f707e25f1 100644
--- a/lib/webpacker/helper.rb
+++ b/lib/webpacker/helper.rb
@@ -9,8 +9,12 @@ module Webpacker::Helper
   # In production mode:
   #   <%= asset_pack_path 'calendar.css' %> # => "/packs/calendar-1016838bab065ae1e122.css"
   def asset_pack_path(name, **options)
-    asset_path(Webpacker::Manifest.lookup(name), **options)
+    path = Webpacker::Configuration.public_output_path
+    file = Webpacker::Manifest.lookup(name)
+    full_path = "#{path}/#{file}"
+    asset_path(full_path, **options)
   end
+
   # Creates a script tag that references the named pack file, as compiled by Webpack per the entries list
   # in config/webpack/shared.js. By default, this list is auto-generated to match everything in
   # app/javascript/packs/*.js. In production mode, the digested reference is automatically looked up.
@@ -25,8 +29,7 @@ def asset_pack_path(name, **options)
   #   <%= javascript_pack_tag 'calendar', 'data-turbolinks-track': 'reload' %> # =>
   #   <script src="/packs/calendar-1016838bab065ae1e314.js" data-turbolinks-track="reload"></script>
   def javascript_pack_tag(*names, **options)
-    sources = names.map { |name|  Webpacker::Manifest.lookup("#{name}#{compute_asset_extname(name, type: :javascript)}") }
-    javascript_include_tag(*sources, **options)
+    javascript_include_tag(*asset_source(names, :javascript), **options)
   end
 
   # Creates a link tag that references the named pack file, as compiled by Webpack per the entries list
@@ -42,8 +45,25 @@ def javascript_pack_tag(*names, **options)
   #   # In production mode:
   #   <%= stylesheet_pack_tag 'calendar', 'data-turbolinks-track': 'reload' %> # =>
   #   <link rel="stylesheet" media="screen" href="/packs/calendar-1016838bab065ae1e122.css" data-turbolinks-track="reload" />
+  #   # In development mode with hot-reloading
+  #   <%= stylesheet_pack_tag('main') %> <% # Default is false for enabled_when_hot_loading%>
+  #   # No output
+  #
+  #   # In development mode with hot-reloading and enabled_when_hot_loading
+  #   # <%= stylesheet_pack_tag('main', enabled_when_hot_loading: true) %>
+  #   <link rel="stylesheet" media="screen" href="/public/webpack/development/calendar-1016838bab065ae1e122.css" />
+  #
   def stylesheet_pack_tag(*names, **options)
-    sources = names.map { |name|  Webpacker::Manifest.lookup("#{name}#{compute_asset_extname(name, type: :stylesheet)}") }
-    stylesheet_link_tag(*sources, **options)
+    return "" if Webpacker::DevServer.hot?
+    stylesheet_link_tag(*asset_source(names, :stylesheet), **options)
   end
+
+  private
+    def asset_source(names, type)
+      output_path_or_url = Webpacker::Configuration.output_path_or_url
+      names.map do |name|
+        path = Webpacker::Manifest.lookup("#{name}#{compute_asset_extname(name, type: type)}")
+        "#{output_path_or_url}/#{path}"
+      end
+    end
 end
diff --git a/lib/webpacker/manifest.rb b/lib/webpacker/manifest.rb
index bcd1d9710..40a76004d 100644
--- a/lib/webpacker/manifest.rb
+++ b/lib/webpacker/manifest.rb
@@ -13,6 +13,10 @@ def file_path
       Webpacker::Configuration.manifest_path
     end
 
+    # Throws an error if the file is not found. If Configuration.compile? then compilation is invoked
+    # the file is missing.
+    # React on Rails users will need to set Configuration.compile? to false as compilation is configured
+    # in the package.json for React on Rails.
     def lookup(name)
       if Webpacker::Configuration.compile?
         compile_and_find!(name)
@@ -21,24 +25,76 @@ def lookup(name)
       end
     end
 
+    # Why does this method exist? Testing? It's not in the README
     def lookup_path(name)
-      Rails.root.join(File.join(Webpacker::Configuration.public_path, lookup(name)))
+      Rails.root.join(File.join(Webpacker::Configuration.output_path, lookup(name)))
     end
 
-    private
-      def find!(name)
-        raise Webpacker::FileLoader::FileLoaderError.new("Webpacker::Manifest.load must be called first") unless instance
-        instance.data[name.to_s] || raise(Webpacker::FileLoader::NotFoundError.new("Can't find #{name} in #{file_path}. Is webpack still compiling?"))
+    # Helper method to determine if the manifest file exists. Maybe Webpack needs to run?
+    # **Used by React on Rails.**
+    def exist?
+      path_object = Webpacker::Configuration.manifest_path
+      path_object.exist?
+    end
+
+    # Find the real file name from the manifest key. Don't throw an error if the file is simply
+    # missing from the manifest. Return nil in that case.
+    # If no manifest file exists, then throw an error.
+    # **Used by React on Rails.**
+    def lookup_no_throw(name)
+      instance.confirm_manifest_exists
+
+      load_instance
+      unless instance
+        raise Webpacker::FileLoader::FileLoaderError.new("Webpacker::Manifest.load must be called first")
       end
+      instance.data[name.to_s]
+    end
 
-      def compile_and_find!(name)
-        Webpacker.compile
-        find!(name)
+    private
+    def find!(name)
+      unless instance
+        raise Webpacker::FileLoader::FileLoaderError.new("Webpacker::Manifest.load must be called first")
       end
+      instance.data[name.to_s] || missing_file_from_manifest_error(name)
+    end
+
+    def missing_file_from_manifest_error(bundle_name)
+      msg = <<-MSG
+        Webpacker can't find #{bundle_name} in your manifest at #{file_path}. Possible causes:
+          1. You are hot reloading.
+          2. You want to set Configuration.compile to true for your environment.
+          3. Webpack has not re-run to reflect updates.
+          4. You have misconfigured Webpacker's config/webpacker.yml file.
+          5. Your Webpack configuration is not creating a manifest.
+      MSG
+      raise(Webpacker::FileLoader::NotFoundError.new(msg))
+    end
+
+    def missing_manifest_file_error(path_object)
+      msg = <<-MSG
+        Webpacker can't find the manifest file: #{path_object}
+        Possible causes:
+          1. You have not invoked webpack.
+          2. You have misconfigured Webpacker's config/webpacker_.yml file.
+          3. Your Webpack configuration is not creating a manifest.
+      MSG
+      raise(Webpacker::FileLoader::NotFoundError.new(msg))
+    end
+
+    def compile_and_find!(name)
+      Webpacker.compile
+      find!(name)
+    end
+  end
+
+  def confirm_manifest_exists
+    raise missing_manifest_file_error(@path) unless File.exist?(@path)
   end
 
   private
-    def load
+
+    def load_data
       return super unless File.exist?(@path)
       JSON.parse(File.read(@path))
     end
diff --git a/test/configuration_test.rb b/test/configuration_test.rb
index c6d55da5a..f2b23cdee 100644
--- a/test/configuration_test.rb
+++ b/test/configuration_test.rb
@@ -3,31 +3,31 @@
 class ConfigurationTest < Minitest::Test
   def test_entry_path
     entry_path = File.join(File.dirname(__FILE__), "test_app/app/javascript", "packs").to_s
-    assert_equal Webpacker::Configuration.entry_path.to_s, entry_path
+    assert_equal entry_path, Webpacker::Configuration.entry_path.to_s
   end
 
   def test_file_path
     file_path = File.join(File.dirname(__FILE__), "test_app/config", "webpacker.yml").to_s
-    assert_equal Webpacker::Configuration.file_path.to_s, file_path
+    assert_equal file_path, Webpacker::Configuration.file_path.to_s
   end
 
   def test_manifest_path
     manifest_path = File.join(File.dirname(__FILE__), "test_app/public/packs", "manifest.json").to_s
-    assert_equal Webpacker::Configuration.manifest_path.to_s, manifest_path
+    assert_equal manifest_path, Webpacker::Configuration.manifest_path.to_s
   end
 
   def test_output_path
     output_path = File.join(File.dirname(__FILE__), "test_app/public/packs").to_s
-    assert_equal Webpacker::Configuration.output_path.to_s, output_path
+    assert_equal output_path, Webpacker::Configuration.output_path.to_s
   end
 
   def test_source
-    assert_equal Webpacker::Configuration.source.to_s, "app/javascript"
+    assert_equal "app/javascript", Webpacker::Configuration.source.to_s
   end
 
   def test_source_path
     source_path = File.join(File.dirname(__FILE__), "test_app/app/javascript").to_s
-    assert_equal Webpacker::Configuration.source_path.to_s, source_path
+    assert_equal source_path, Webpacker::Configuration.source_path.to_s
   end
 
   def test_compile?
diff --git a/test/dev_server_test.rb b/test/dev_server_test.rb
new file mode 100644
index 000000000..5c59dacbb
--- /dev/null
+++ b/test/dev_server_test.rb
@@ -0,0 +1,56 @@
+require "webpacker_test"
+
+class DevServerTest < Minitest::Test
+  require "webpacker_test"
+
+  def check_assertion
+    stub_value = ActiveSupport::StringInquirer.new("development")
+    Webpacker.stub(:env, stub_value) do
+      Webpacker::Configuration.reset
+      Webpacker::DevServer.reset
+      result = yield
+      assert_equal(result[0], result[1])
+    end
+    Webpacker::Configuration.reset
+    Webpacker::DevServer.reset
+  end
+
+  def test_dev_server?
+    check_assertion { [true, Webpacker::DevServer.dev_server?] }
+  end
+
+  def test_dev_server_host
+    check_assertion { ["localhost", Webpacker::DevServer.host] }
+  end
+
+  def test_dev_server_port
+    check_assertion { [8080, Webpacker::DevServer.port] }
+  end
+
+  def test_dev_server_hot?
+    check_assertion { [false, Webpacker::DevServer.hot?] }
+
+    ENV.stub(:[], "TRUE") do
+      check_assertion { [true, Webpacker::DevServer.hot?] }
+    end
+
+    ENV.stub(:[], "FALSE") do
+      check_assertion { [false, Webpacker::DevServer.hot?] }
+    end
+    ENV.stub(:[], "true") do
+      check_assertion { [true, Webpacker::DevServer.hot?] }
+    end
+  end
+
+  def test_dev_server_https?
+    check_assertion { [false, Webpacker::DevServer.https?] }
+  end
+
+  def test_dev_server_protocol?
+    check_assertion { ["http", Webpacker::DevServer.protocol] }
+  end
+
+  def test_base_url?
+    check_assertion { ["http://localhost:8080", Webpacker::DevServer.base_url] }
+  end
+end
diff --git a/test/helper_test.rb b/test/helper_test.rb
index 527968b24..1215581e6 100644
--- a/test/helper_test.rb
+++ b/test/helper_test.rb
@@ -7,29 +7,39 @@ def setup
   end
 
   def test_asset_pack_path
-    assert_equal @view.asset_pack_path("bootstrap.js"), "/packs/bootstrap-300631c4f0e0f9c865bc.js"
-    assert_equal @view.asset_pack_path("bootstrap.css"), "/packs/bootstrap-c38deda30895059837cf.css"
+    assert_equal "/packs/bootstrap-300631c4f0e0f9c865bc.js", @view.asset_pack_path("bootstrap.js")
+    assert_equal "/packs/bootstrap-c38deda30895059837cf.css", @view.asset_pack_path("bootstrap.css")
   end
 
   def test_javascript_pack_tag
     script = %(<script src="/packs/bootstrap-300631c4f0e0f9c865bc.js"></script>)
-    assert_equal @view.javascript_pack_tag("bootstrap.js"), script
+    assert_equal script, @view.javascript_pack_tag("bootstrap.js")
   end
 
   def test_javascript_pack_tag_splat
     script = %(<script src="/packs/bootstrap-300631c4f0e0f9c865bc.js" defer="defer"></script>\n) +
       %(<script src="/packs/application-k344a6d59eef8632c9d1.js" defer="defer"></script>)
-    assert_equal @view.javascript_pack_tag("bootstrap.js", "application.js", defer: true), script
+    assert_equal script, @view.javascript_pack_tag("bootstrap.js", "application.js", defer: true)
   end
 
   def test_stylesheet_pack_tag
     style = %(<link rel="stylesheet" media="screen" href="/packs/bootstrap-c38deda30895059837cf.css" />)
-    assert_equal @view.stylesheet_pack_tag("bootstrap.css"), style
+    assert_equal style, @view.stylesheet_pack_tag("bootstrap.css")
   end
 
   def test_stylesheet_pack_tag_splat
     style = %(<link rel="stylesheet" media="all" href="/packs/bootstrap-c38deda30895059837cf.css" />\n) +
       %(<link rel="stylesheet" media="all" href="/packs/application-dd6b1cd38bfa093df600.css" />)
-    assert_equal @view.stylesheet_pack_tag("bootstrap.css", "application.css", media: "all"), style
+    assert_equal style, @view.stylesheet_pack_tag("bootstrap.css", "application.css", media: "all")
+  end
+
+  def test_stylesheet_pack_tag_outputs_nothing_for_hot
+    Webpacker::DevServer.stub(:hot?, true) do
+      # Webpacker::Configuration.reset
+      # Webpacker::DevServer.reset
+      assert_equal "", @view.stylesheet_pack_tag("bootstrap.css")
+    end
+    # Webpacker::Configuration.reset
+    # Webpacker::DevServer.reset
   end
 end
diff --git a/test/manifest_test.rb b/test/manifest_test.rb
index 528064800..751d7df42 100644
--- a/test/manifest_test.rb
+++ b/test/manifest_test.rb
@@ -3,30 +3,75 @@
 class ManifestTest < Minitest::Test
   def test_file_path
     file_path = File.join(File.dirname(__FILE__), "test_app/public/packs", "manifest.json").to_s
-    assert_equal Webpacker::Manifest.file_path.to_s, file_path
+    assert_equal(Webpacker::Manifest.file_path.to_s, file_path)
   end
 
   def test_lookup_exception
     manifest_path = File.join(File.dirname(__FILE__), "test_app/public/packs", "manifest.json").to_s
     asset_file = "calendar.js"
+    msg = <<-MSG
+        Webpacker can't find #{asset_file} in your manifest at #{manifest_path}. Possible causes:
+          1. You are hot reloading.
+          2. You want to set Configuration.compile to true for your environment.
+          3. Webpack has not re-run to reflect updates.
+          4. You have misconfigured Webpacker's config/webpacker.yml file.
+          5. Your Webpack configuration is not creating a manifest.
+    MSG
 
     Webpacker::Configuration.stub :compile?, false do
       error = assert_raises Webpacker::FileLoader::NotFoundError do
         Webpacker::Manifest.lookup(asset_file)
       end
 
-      assert_equal error.message, "Can't find #{asset_file} in #{manifest_path}. Is webpack still compiling?"
+      assert_equal(error.message, msg)
     end
   end
 
   def test_lookup_success
     asset_file = "bootstrap.js"
-    assert_equal Webpacker::Manifest.lookup(asset_file), "/packs/bootstrap-300631c4f0e0f9c865bc.js"
+    assert_equal("bootstrap-300631c4f0e0f9c865bc.js", Webpacker::Manifest.lookup(asset_file))
   end
 
   def test_lookup_path
     file_path = File.join(File.dirname(__FILE__), "test_app/public/packs", "bootstrap-300631c4f0e0f9c865bc.js").to_s
     asset_file = "bootstrap.js"
-    assert_equal Webpacker::Manifest.lookup_path(asset_file).to_s, file_path
+    assert_equal(file_path, Webpacker::Manifest.lookup_path(asset_file).to_s)
+  end
+
+  def test_file_not_existing
+    begin
+      file_path = File.join(File.dirname(__FILE__), "test_app/public/packs", "manifest.json")
+      temp_path = "#{file_path}.backup"
+      FileUtils.mv(file_path, temp_path)
+      # Point of this test is to ensure no crash
+      Webpacker::Manifest.load_instance
+      assert_equal({}, Webpacker::Manifest.instance.data)
+    ensure
+      FileUtils.mv(temp_path, file_path)
+      Webpacker::Manifest.instance = nil
+      Webpacker::Manifest.load_instance
+    end
+  end
+
+  def test_lookup_success
+    asset_file = "bootstrap.js"
+    assert_equal("bootstrap-300631c4f0e0f9c865bc.js", Webpacker::Manifest.lookup(asset_file))
+  end
+
+  def test_confirm_manifest_exists_for_existing
+    Webpacker::Manifest.instance.confirm_manifest_exists
+  end
+
+  def test_confirm_manifest_exists_for_missing
+    assert_raises do
+      Webpacker::Manifest.stub :path, "non-existent-file" do
+        confirm_manifest_exists
+      end
+    end
+  end
+
+  def test_lookup_no_throw
+    value = Webpacker::Manifest.lookup_no_throw("non-existent-bundle.js")
+    assert_equal(nil, value)
   end
 end
diff --git a/test/test_app/public/packs/manifest.json b/test/test_app/public/packs/manifest.json
index f7b77dd63..a5b6cb8e5 100644
--- a/test/test_app/public/packs/manifest.json
+++ b/test/test_app/public/packs/manifest.json
@@ -1,6 +1,6 @@
 {
-  "bootstrap.css": "/packs/bootstrap-c38deda30895059837cf.css",
-  "application.css": "/packs/application-dd6b1cd38bfa093df600.css",
-  "bootstrap.js": "/packs/bootstrap-300631c4f0e0f9c865bc.js",
-  "application.js": "/packs/application-k344a6d59eef8632c9d1.js"
+  "bootstrap.css": "bootstrap-c38deda30895059837cf.css",
+  "application.css": "application-dd6b1cd38bfa093df600.css",
+  "bootstrap.js": "bootstrap-300631c4f0e0f9c865bc.js",
+  "application.js": "application-k344a6d59eef8632c9d1.js"
 }
diff --git a/test/webpacker_test.rb b/test/webpacker_test.rb
index f05871147..02547fb18 100644
--- a/test/webpacker_test.rb
+++ b/test/webpacker_test.rb
@@ -5,6 +5,11 @@
 require "rails/test_help"
 require "webpacker"
 
+if ENV["USE_PRY"]
+  require "pry"
+  require "awesome_print"
+end
+
 module TestApp
   class Application < ::Rails::Application
     config.root = File.join(File.dirname(__FILE__), "test_app")