Add Rails integration test

test/integration/rails_integration_test.rb

@@ -0,0 +1,122 @@
+# frozen_string_literal: true
+
+require "test_helper"
+require "tempfile"
+require "fileutils"
+require "open3"
+
+class RailsIntegrationTest < ActiveSupport::TestCase
+  CommandFailed = Class.new(StandardError)
+
+  test "running a job in a Rails app works" do
+    # This test is slow, because it has to install gems and generate an entire Rails app.
+    in_dummy_rails_app_with_job_iteration do |_dir|
+      puts "Writing app/jobs/example_job.rb" if ENV["DEBUG"]
+      File.write("app/jobs/example_job.rb", <<~RUBY)
+        class ExampleJob < ApplicationJob
+          include JobIteration::Iteration
+
+          def build_enumerator(cursor:)
+            enumerator_builder.array(["it works"], cursor: cursor)
+          end
+
+          def each_iteration(string)
+            puts string
+          end
+        end
+      RUBY
+
+      output = run_or_raise("bin/rails", "runner", "ExampleJob.perform_now")
+      assert_includes(output, "it works")
+    end
+  end
+
+  private
+
+  def in_dummy_rails_app_with_job_iteration
+    Dir.mktmpdir do |dir|
+      Dir.chdir(dir) do |dir|
+        dir = File.join(dir, "dummy")
+        FileUtils.mkdir(dir)
+        Dir.chdir(dir) do |dir|
+          with_env(ENV.reject { |k, _v| k == "BUNDLE_GEMFILE" }) do # Don't use the Gemfile override set in CI.
+            run_or_raise("bundle", "init")
+
+            # It is unclear why we need to do this, but otherwise it blows up with:
+            #   Could not find <the gems below> in any of the sources (Bundler::GemNotFound)
+            run_or_raise("gem", "install", "nio4r")
+            run_or_raise("gem", "install", "websocket-driver")
+            run_or_raise("gem", "install", "date")
+            run_or_raise("gem", "install", "racc")
+
+            # It is also unclear why we need to --skip-install, lock, and install, instead of just using `bundle add`,
+            # but, again, otherwise it blows up with the same error as above.
+            run_or_raise("bundle", "add", "rails", "--version", rails_version.to_s, "--skip-install")
+            run_or_raise("bundle", "lock")
+            run_or_raise("bundle", "install")
+
+            run_or_raise(
+              "rails",
+              "new",
+              ".",
+              "--force",
+              # We should switch to `--minimal --no-skip-active-job` once the oldest supported Rails version supports it
+              # https://github.com/rails/rails/blob/a4581b53aae93a8dd3205abae0630398cbce9204/railties/lib/rails/generators/app_base.rb#L35-L88
+              "--skip-yarn",
+              "--skip-git",
+              "--skip-action-mailer",
+              "--skip-action-storage",
+              "--skip-puma",
+              "--skip-action-cable",
+              "--skip-sprockets",
+              "--skip-spring",
+              "--skip-listen",
+              "--skip-coffee",
+              "--skip-javascript",
+              "--skip-test",
+              "--skip-system-test",
+              "--skip-bootsnap",
+            )
+            # `bundle add` doesn't support path: sources, so we'll append it manually
+            puts "Simulating `bundle add job-iteration` with path: to this repo." if ENV["DEBUG"]
+            File.open("Gemfile", "a") { |f| f.puts "gem 'job-iteration', path: '#{Bundler.root}'" }
+            run_or_raise("bundle", "install")
+
+            yield dir
+          end
+        end
+      end
+    end
+  end
+
+  def run_or_raise(*args, **kwargs, &block)
+    puts "Running: #{args.join(" ")}" if ENV["DEBUG"]
+
+    stdout_and_stderr, status = Open3.capture2e(
+      # ENV.to_hash.merge({"COLUMNS" => "1000"})
+      { "COLUMNS" => "1000" }, # Otherwise output is weirdly wrapped.
+      *args,
+      **kwargs,
+      &block
+    )
+    raise CommandFailed, stdout_and_stderr unless status.success?
+
+    puts stdout_and_stderr if ENV["DEBUG"]
+
+    stdout_and_stderr
+  end
+
+  def rails_version
+    # We're going to install Rails in the dummy app, so we need to know the version to install.
+    # We don't depend on Rails though, so read the version of Active Support instead, since they always match.
+    Gem.loaded_specs.fetch("activesupport").version
+  end
+
+  def with_env(env)
+    original_env = ENV.to_hash
+    ENV.replace(env)
+    yield
+  ensure
+    ENV.replace(original_env)
+  end
+end