Test Rails Controller README example

Author: sambostock

README.md

@@ -63,6 +63,7 @@ requests.
 
 You can use the `Server#handle_json` method to handle requests.
 
+<!-- SNIPPET ID: rails_controller -->
 ```ruby
 class ApplicationController < ActionController::Base
 

test/fixtures/files/code_snippet_wrappers/readme/rails_controller.rb

@@ -0,0 +1,50 @@
+# frozen_string_literal: true
+
+require "json"
+require "stringio"
+
+# For simplicity, we'll stub out the relevant parts of the Rails API.
+module ActionController
+  class Base
+    class Request
+      attr_reader :body
+
+      def initialize(body)
+        @body = StringIO.new(body)
+      end
+    end
+
+    class User
+      attr_reader :id
+
+      def initialize(id:)
+        @id = id
+      end
+    end
+
+    attr_reader :request
+
+    def initialize(request_body)
+      @request = Request.new(request_body)
+    end
+
+    def render(json:) = json
+
+    private
+
+    def current_user = User.new(id: 1)
+  end
+end
+
+# We need to create the minimal surrounding resources to run the code snippet
+require "mcp"
+
+SomeTool    = MCP::Tool.define(name: "some_tool")    { MCP::Tool::Response.new(content: "some_tool response") }
+AnotherTool = MCP::Tool.define(name: "another_tool") { MCP::Tool::Response.new(content: "another_tool response") }
+MyPrompt    = MCP::Prompt.define(name: "my_prompt")  { MCP::Prompt::Result.new }
+
+require_relative "code_snippet"
+
+puts ApplicationController.new(
+  { jsonrpc: "2.0", id: "1", method: "ping" }.to_json,
+).index

test/integration/readme_code_snippets_test.rb

@@ -0,0 +1,58 @@
+# frozen_string_literal: true
+
+require "test_helper"
+
+require "fileutils"
+require "open3"
+require "tempfile"
+require "timeout"
+
+require "readme_test_helper"
+
+# Run tests on the code snippets in the README.md file to ensure they work as expected.
+# These are not intended to be comprehensive; they are just sanity checks.
+class ReadmeCodeSnippetsTest < ActiveSupport::TestCase
+  include ReadmeTestHelper
+
+  make_my_diffs_pretty!
+
+  test "Rails Controller example handles requests" do
+    assert_json_lines(
+      [
+        { jsonrpc: "2.0", id: "1", result: {} },
+      ],
+      run_code_snippet("rails_controller"),
+    )
+  end
+
+  private
+
+  def assert_json_lines(expected, actual, message = "Expected the given JSON lines")
+    assert_equal(
+      expected,
+      actual.lines(chomp: true).map { JSON.parse(_1, symbolize_names: true) },
+      message,
+    )
+  end
+
+  def run_code_snippet(code_snippet_name)
+    Dir.mktmpdir do |dir|
+      Dir.chdir(dir) do
+        File.write("code_snippet.rb", extract_readme_code_snippet(code_snippet_name))
+        File.write("test.rb", file_fixture("code_snippet_wrappers/readme/#{code_snippet_name}.rb").read)
+
+        stdout, stderr, status = Timeout.timeout(5) { Open3.capture3("ruby", "test.rb") }
+        assert_predicate(status, :success?, "Expected test.rb to exit with success, but got exit status #{status.exitstatus}\n\nSTDOUT: #{stdout}\n\nSTDERR: #{stderr}")
+        assert_empty(stderr, "Expected no stderr in: #{stderr}")
+        refute_empty(stdout, "Expected stdout not to be empty")
+
+        normalize_stdout(stdout)
+      end
+    end
+  end
+
+  def normalize_stdout(stdout)
+    stdout
+      .gsub(/duration: \d+\.\d+(?:e-\d+)?/, "duration: 1.23") # e.g. duration: 1.23456789012345678-05
+  end
+end