diff --git a/.gitignore b/.gitignore
index 207100846..6b4101e28 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,4 +1,5 @@
 /.bundle
 /pkg
 /test/test_app/log
+/test/test_app/tmp
 node_modules
diff --git a/README.md b/README.md
index 2ba8ed34f..77b49e836 100644
--- a/README.md
+++ b/README.md
@@ -271,7 +271,7 @@ foreman start
 ```
 
 By default, `webpack-dev-server` listens on `0.0.0.0` that means listening
-on all IP addresses available on your system: LAN IP address, localhost, 127.0.0.1 etc. 
+on all IP addresses available on your system: LAN IP address, localhost, 127.0.0.1 etc.
 However, we use `localhost` as default hostname for serving assets in browser
 and if you want to change that, for example on cloud9 you can do so
 by changing host set in `config/webpacker.yml`.
@@ -360,8 +360,14 @@ development:
     host: 0.0.0.0
     port: 8080
     https: false
+    hmr: false
 ```
 
+If you have hmr 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
@@ -445,6 +451,16 @@ You can checkout these links on this subject:
 - https://webpack.js.org/configuration/dev-server/#devserver-hot
 - https://webpack.js.org/guides/hmr-react/
 
+If you are using hot reloading, you should either set the `dev_server/hmr` key to TRUE or set the
+ENV value `WEBPACKER_HMR=TRUE`. That way, your stylesheet pack tag will do **nothing** because you
+need your styles inlined in your JavaScript for hot reloading to work properly.
+
+### Live Reloading or Static Reloading
+Live Reloading is having your assets for development provided by the webpack-dev-server.
+
+You can override the the presence of the `dev_server` setup by setting ENV value: `WEBPACKER_DEV_SERVER=FALSE`.
+
+You might do this if you are switching back and forth between statically compiling files during development and trying to get hot reloading to work.
 
 ## Linking Styles, Images and Fonts
 
@@ -593,9 +609,9 @@ 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:
+If you need more advanced React-integration, like server rendering, redux, or react-router, see [shakacode/react_on_rails](https://github.com/shakacode/react_on_rails), [react-rails](https://github.com/reactjs/react-rails), and [webpacker-react](https://github.com/renchap/webpacker-react).
+
+If you're not concerned with view helpers to pass props or server rendering, can do it yourself:
 
 ```erb
 <%# views/layouts/application.html.erb %>
diff --git a/lib/install/config/webpack/development.js b/lib/install/config/webpack/development.js
index 7247e31aa..88bebac03 100644
--- a/lib/install/config/webpack/development.js
+++ b/lib/install/config/webpack/development.js
@@ -1,5 +1,6 @@
 // Note: You must restart bin/webpack-dev-server for changes to take effect
 
+const webpack = require('webpack')
 const merge = require('webpack-merge')
 const sharedConfig = require('./shared.js')
 const { settings, output } = require('./configuration.js')
@@ -16,6 +17,7 @@ module.exports = merge(sharedConfig, {
     https: settings.dev_server.https,
     host: settings.dev_server.host,
     port: settings.dev_server.port,
+    hot: settings.dev_server.hmr,
     contentBase: output.path,
     publicPath: output.publicPath,
     compress: true,
@@ -27,5 +29,10 @@ module.exports = merge(sharedConfig, {
     stats: {
       errorDetails: true
     }
-  }
+  },
+
+  plugins: settings.dev_server.hmr ? [
+    new webpack.HotModuleReplacementPlugin(),
+    new webpack.NamedModulesPlugin()
+  ] : []
 })
diff --git a/lib/install/config/webpack/shared.js b/lib/install/config/webpack/shared.js
index 6feacb716..244efd65e 100644
--- a/lib/install/config/webpack/shared.js
+++ b/lib/install/config/webpack/shared.js
@@ -27,8 +27,7 @@ module.exports = {
 
   output: {
     filename: '[name].js',
-    path: output.path,
-    publicPath: output.publicPath
+    path: output.path
   },
 
   module: {
@@ -38,10 +37,7 @@ module.exports = {
   plugins: [
     new webpack.EnvironmentPlugin(JSON.parse(JSON.stringify(env))),
     new ExtractTextPlugin(env.NODE_ENV === 'production' ? '[name]-[contenthash].css' : '[name].css'),
-    new ManifestPlugin({
-      publicPath: output.publicPath,
-      writeToFileEmit: true
-    })
+    new ManifestPlugin({ writeToFileEmit: true })
   ],
 
   resolve: {
diff --git a/lib/install/config/webpacker.yml b/lib/install/config/webpacker.yml
index 8fcb01506..00c6e80ed 100644
--- a/lib/install/config/webpacker.yml
+++ b/lib/install/config/webpacker.yml
@@ -33,6 +33,7 @@ development:
     host: localhost
     port: 8080
     https: false
+    hmr: false
 
 test:
   <<: *default
diff --git a/lib/webpacker.rb b/lib/webpacker.rb
index 958eff25d..bdb4f134f 100644
--- a/lib/webpacker.rb
+++ b/lib/webpacker.rb
@@ -20,6 +20,7 @@ def env
 require "webpacker/logger"
 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/compiler.rb b/lib/webpacker/compiler.rb
index d85775e61..bf8eb9dc3 100644
--- a/lib/webpacker/compiler.rb
+++ b/lib/webpacker/compiler.rb
@@ -1,6 +1,4 @@
 require "open3"
-require "webpacker/env"
-require "webpacker/configuration"
 
 module Webpacker::Compiler
   extend self
@@ -13,6 +11,8 @@ module Webpacker::Compiler
   mattr_accessor(:watched_paths) { [] }
 
   def compile
+    return if Webpacker::DevServer.running?
+
     if stale?
       cache_source_timestamp
       run_webpack
diff --git a/lib/webpacker/configuration.rb b/lib/webpacker/configuration.rb
index c04ce8bdd..5188966d3 100644
--- a/lib/webpacker/configuration.rb
+++ b/lib/webpacker/configuration.rb
@@ -8,8 +8,12 @@ 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
@@ -61,7 +65,7 @@ def defaults
 
   private
     def load
-      return super unless File.exist?(@path)
+      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..0e72395c2
--- /dev/null
+++ b/lib/webpacker/dev_server.rb
@@ -0,0 +1,47 @@
+module Webpacker::DevServer
+  extend self
+
+  def running?
+    socket = Socket.tcp(host, port, connect_timeout: 1)
+    socket.close
+    true
+
+  rescue Errno::ECONNREFUSED, NoMethodError
+    false
+  end
+
+  def hmr?
+    case ENV["WEBPACKER_HMR"]
+    when /true/i then true
+    when /false/i then false
+    else fetch(:hmr)
+    end
+
+  rescue NoMethodError
+    false
+  end
+
+  def host
+    fetch(:host)
+  end
+
+  def port
+    fetch(:port)
+  end
+
+  def https?
+    fetch(:https)
+  end
+
+  def protocol
+    https? ? "https" : "http"
+  end
+
+  def base_url
+    "#{protocol}://#{host}:#{port}"
+  end
+
+  def fetch(key)
+    Webpacker::Configuration.data[:dev_server][key] || Webpacker::Configuration.defaults[:dev_server][key]
+  end
+end
diff --git a/lib/webpacker/file_loader.rb b/lib/webpacker/file_loader.rb
index 42eca50a0..44c8915c0 100644
--- a/lib/webpacker/file_loader.rb
+++ b/lib/webpacker/file_loader.rb
@@ -4,13 +4,29 @@ 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)
-      self.instance = new(path)
+      if instance.nil? || !production_env? || !file_cached?(path)
+        self.instance = new(path)
+      end
+    end
+
+    def file_path
+      raise FileLoaderError.new("Subclass of Webpacker::FileLoader should override this method")
     end
 
+    private
+      def file_cached?(path)
+        File.exist?(path) && self.instance.mtime == File.mtime(path)
+      end
+
+      # Prefer the NODE_ENV to the rails env.
+      def production_env?
+        (ENV["NODE_ENV"].presence || Rails.env) == "production"
+      end
+
     protected
       def ensure_loaded_instance(klass)
         raise Webpacker::FileLoader::FileLoaderError.new("#{klass.name}#load must be called first") unless instance
@@ -20,6 +36,7 @@ def ensure_loaded_instance(klass)
   private
     def initialize(path)
       @path = path
+      @mtime = File.exist?(path) ? File.mtime(path) : nil
       @data = load
     end
 
diff --git a/lib/webpacker/helper.rb b/lib/webpacker/helper.rb
index 0034ed099..ddb492ecc 100644
--- a/lib/webpacker/helper.rb
+++ b/lib/webpacker/helper.rb
@@ -9,8 +9,9 @@ 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)
+    asset_path(Webpacker::Manifest.pack_path(name), **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.
@@ -41,13 +42,21 @@ 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
+  #
   def stylesheet_pack_tag(*names, **options)
-    stylesheet_link_tag(*sources_from_pack_manifest(names, type: :stylesheet), **options)
+    if Webpacker::DevServer.hmr?
+      ""
+    else
+      stylesheet_link_tag(*sources_from_pack_manifest(names, type: :stylesheet), **options)
+    end
   end
 
   private
     def sources_from_pack_manifest(names, type:)
-      names.map { |name| Webpacker::Manifest.lookup(pack_name_with_extension(name, type: type)) }
+      names.map { |name| Webpacker::Manifest.pack_path(pack_name_with_extension(name, type: type)) }
     end
 
     def pack_name_with_extension(name, type:)
diff --git a/lib/webpacker/manifest.rb b/lib/webpacker/manifest.rb
index 015b65f7f..fd51f362e 100644
--- a/lib/webpacker/manifest.rb
+++ b/lib/webpacker/manifest.rb
@@ -17,31 +17,90 @@ def file_path
       Webpacker::Configuration.manifest_path
     end
 
-    def lookup(name)
+    # Converts the "name" (aka the pack or bundle name) to to the full path for use in a browser.
+    def pack_path(name)
+      relative_pack_path = "#{Webpacker::Configuration.public_output_path}/#{lookup(name)}"
+
+      if Webpacker::DevServer.running?
+        "#{Webpacker::DevServer.base_url}/#{relative_pack_path}"
+      else
+        relative_pack_path.starts_with?("/") ? relative_pack_path : "/#{relative_pack_path}"
+      end
+    end
+
+    # Converts the "name" (aka the pack or bundle name) to the possibly hashed name per a manifest.
+    #
+    # If Configuration.compile? then compilation is invoked the file is missing.
+    #
+    # Options
+    # throw_if_missing: default is true. If false, then nill is returned if the file is missing.
+    def lookup(name, throw_if_missing: true)
+      instance.confirm_manifest_exists
+
       if Webpacker::Configuration.compile?
-        compile_and_find!(name)
+        compile_and_find!(name, throw_if_missing: throw_if_missing)
       else
-        find!(name)
+        # Since load checks a `mtime` on the manifest for a non-production env before loading,
+        # we should always call this before a call to `find!` since one may be using
+        # `webpack -w` and a file may have been added to the manifest since Rails first started.
+        load
+        raise Webpacker::FileLoader::FileLoaderError.new("Webpacker::Manifest.load must be called first") unless instance
+
+        return find!(name, throw_if_missing: throw_if_missing)
       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)
+      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.
+Your manifest contains:
+#{instance.data.to_json}
+        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 find!(name, throw_if_missing: true)
         ensure_loaded_instance(self)
-        instance.data[name.to_s] ||
-          raise(Webpacker::FileLoader::NotFoundError.new("Can't find #{name} in #{file_path}. Is webpack still compiling?"))
+        value = instance.data[name.to_s]
+        return value if value.present?
+
+        if throw_if_missing
+          missing_file_from_manifest_error(name)
+        end
       end
 
-      def compile_and_find!(name)
+      def compile_and_find!(name, throw_if_missing: true)
         Webpacker.logger.tagged("Webpacker") { Webpacker.compile }
-        find!(name)
+        find!(name, throw_if_missing: throw_if_missing)
       end
   end
 
+  def confirm_manifest_exists
+    raise missing_manifest_file_error(@path) unless File.exist?(@path)
+  end
+
   private
     def load
       return super unless File.exist?(@path)
diff --git a/test/compiler_test.rb b/test/compiler_test.rb
index 3059ae6ac..979c5fa67 100644
--- a/test/compiler_test.rb
+++ b/test/compiler_test.rb
@@ -16,7 +16,7 @@ def test_watched_paths
   end
 
   def test_freshness
-    assert Webpacker::Compiler.stale?
-    assert !Webpacker::Compiler.fresh?
+    refute Webpacker::Compiler.stale?
+    refute !Webpacker::Compiler.fresh?
   end
 end
diff --git a/test/configuration_test.rb b/test/configuration_test.rb
index dc1d96f6c..bb91a64c1 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_cache_path
diff --git a/test/dev_server_test.rb b/test/dev_server_test.rb
new file mode 100644
index 000000000..260a69241
--- /dev/null
+++ b/test/dev_server_test.rb
@@ -0,0 +1,61 @@
+require "webpacker_test"
+
+class DevServerTest < Minitest::Test
+  require "webpacker_test"
+
+  def reset
+    Webpacker::Configuration.instance_variable_set(:@defaults, nil)
+    Webpacker::Configuration.instance_variable_set(:@instance, nil)
+  end
+
+  def check_assertion
+    reset
+    stub_value = ActiveSupport::StringInquirer.new("development")
+    Webpacker.stub(:env, stub_value) do
+      Webpacker::Configuration.stub(:data, dev_server: {}) do
+        result = yield
+        assert_equal(result[0], result[1])
+      end
+    end
+    reset
+  end
+
+  def test_dev_server?
+    check_assertion { [false, Webpacker::DevServer.running?] }
+  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_hmr?
+    check_assertion { [false, Webpacker::DevServer.hmr?] }
+
+    ENV.stub(:[], "TRUE") do
+      check_assertion { [true, Webpacker::DevServer.hmr?] }
+    end
+
+    ENV.stub(:[], "FALSE") do
+      check_assertion { [false, Webpacker::DevServer.hmr?] }
+    end
+    ENV.stub(:[], "true") do
+      check_assertion { [true, Webpacker::DevServer.hmr?] }
+    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..2fe0e3a0e 100644
--- a/test/helper_test.rb
+++ b/test/helper_test.rb
@@ -7,29 +7,35 @@ 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(:hmr?, true) do
+      assert_equal "", @view.stylesheet_pack_tag("bootstrap.css")
+    end
   end
 end
diff --git a/test/manifest_test.rb b/test/manifest_test.rb
index 528064800..eb0ce1cb3 100644
--- a/test/manifest_test.rb
+++ b/test/manifest_test.rb
@@ -3,30 +3,82 @@
 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.
+Your manifest contains:
+#{Webpacker::Manifest.instance.data.to_json}
+    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(msg, error.message)
     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
+      assert_equal({}, Webpacker::Manifest.instance.data)
+    ensure
+      FileUtils.mv(temp_path, file_path)
+      Webpacker::Manifest.instance = nil
+      Webpacker::Manifest.load
+    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_missing_file
+    value = Webpacker::Manifest.lookup("non-existent-bundle.js", throw_if_missing: false)
+    assert_nil(value)
+  end
+
+  def test_lookup_no_throw_file_exists
+    file_path = "bootstrap-300631c4f0e0f9c865bc.js"
+    asset_file = "bootstrap.js"
+    assert_equal(file_path, Webpacker::Manifest.lookup(asset_file, throw_if_missing: false))
   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"
 }