added specs

plugin.rb

@@ -97,6 +97,8 @@ after_initialize do
   end
 
   add_to_class(::Sprockets::DirectiveProcessor, :process_require_tree_discourse_directive) do |path = "."|
+    raise ArgumentError, "path cannot be empty" if path == "."
+
     discourse_asset_path = "#{Rails.root}/app/assets/javascripts/"
     path = File.expand_path(path, discourse_asset_path)
     stat = @environment.stat(path)

spec/extensions/sprockets_directive_spec.rb

@@ -0,0 +1,55 @@
+# frozen_string_literal: true
+
+require_relative '../plugin_helper'
+
+describe "Sprockets: require_tree_discourse directive" do
+  let(:discourse_asset_path) {
+   "#{Rails.root}/app/assets/javascripts/"
+  }
+  let(:fixture_asset_path) {
+    "#{Rails.root}/plugins/discourse-custom-wizard/spec/fixtures/sprockets/"
+  }
+  let(:test_file_contents) {
+    "console.log('hello')"
+  }
+  let(:resolved_file_contents) {
+   File.read(
+    "#{Rails.root}/plugins/discourse-custom-wizard/spec/fixtures/sprockets/resolved_js_file_contents.txt"
+   )
+  }
+
+  before do
+    @env ||= Sprockets::Environment.new
+    discourse_asset_path = "#{Rails.root}/app/assets/javascripts/"
+    fixture_asset_path = "#{Rails.root}/plugins/discourse-custom-wizard/spec/fixtures/sprockets/"
+    @env.append_path(discourse_asset_path)
+    @env.append_path(fixture_asset_path)
+    @env.cache = {}
+  end
+
+  def create_tmp_folder_and_run(path, file_contents, &block)
+    dir = File.dirname(path)
+    unless File.directory?(dir)
+      FileUtils.mkdir_p(dir)
+    end
+
+    File.new(path, 'w')
+    File.write(path, file_contents)
+    yield block if block_given?
+    File.delete(path)
+  end
+
+  it "includes assets from the discourse core" do
+    create_tmp_folder_and_run("#{discourse_asset_path}/sptest/test.js", test_file_contents) do
+      expect(@env.find_asset("require_tree_discourse_test.js").to_s).to eq(resolved_file_contents)
+    end
+  end
+
+  it "throws ArgumentError if path is empty" do
+    expect { @env.find_asset("require_tree_discourse_empty.js") }.to raise_error(ArgumentError).with_message("path cannot be empty")
+  end
+
+  it "throws ArgumentError if path is non non-existent" do
+    expect { @env.find_asset("require_tree_discourse_non_existant.js") }.to raise_error(ArgumentError)
+  end
+end

spec/fixtures/sprockets/require_tree_discourse_empty.js

@@ -0,0 +1 @@
+//= require_tree_discourse 

spec/fixtures/sprockets/require_tree_discourse_non_existant.js

@@ -0,0 +1 @@
+//= require_tree_discourse dummy_path

spec/fixtures/sprockets/require_tree_discourse_test.js

@@ -0,0 +1 @@
+//= require_tree_discourse sptest

spec/fixtures/sprockets/resolved_js_file_contents.txt

@@ -0,0 +1,3 @@
+eval("define(\"sptest/test\", [], function () {\n  \"use strict\";\n\n  console.log('hello');\n});" + "\n//# sourceURL=sptest/test");
+;
+eval("" + "\n//# sourceURL=require_tree_discourse_test");