test: Add active_job spec harness scaffolding

Introduce sentry-rails/spec/active_job/ with the adapter-agnostic
harness, FailingJob fixture, and composing shared example. No backend
wiring yet — that lands in a follow-up.

Refs #2933.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: solnic

sentry-rails/spec/active_job/shared_examples/sentry_instrumented_backend.rb

@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+RSpec.shared_examples "a Sentry-instrumented ActiveJob backend" do
+  it "captures an error event when a job fails" do
+    expect do
+      Sentry::Specs::ActiveJob::FailingJob.perform_later
+      drain
+    end.to raise_error(Sentry::Specs::ActiveJob::FailingJob::Boom)
+
+    event = last_sentry_event
+    expect(event).not_to be_nil
+
+    exception = extract_sentry_exceptions(event).first
+    expect(exception.type).to eq("Sentry::Specs::ActiveJob::FailingJob::Boom")
+  end
+end

sentry-rails/spec/active_job/support/harness.rb

@@ -0,0 +1,40 @@
+# frozen_string_literal: true
+
+RSpec.shared_context "active_job backend harness" do |adapter:|
+  before do
+    make_basic_app
+    setup_sentry_test
+
+    @previous_queue_adapter = ::ActiveJob::Base.queue_adapter
+    ::ActiveJob::Base.queue_adapter = adapter
+
+    boot_adapter(adapter)
+  end
+
+  after do
+    reset_adapter(adapter)
+
+    ::ActiveJob::Base.queue_adapter = @previous_queue_adapter
+
+    teardown_sentry_test
+  end
+
+  def boot_adapter(_adapter)
+    # Per-adapter setup hook. Backends extend this when they need to load
+    # schemas, start supervisors, or otherwise prepare the environment.
+  end
+
+  def reset_adapter(_adapter)
+    # Per-adapter teardown hook. Backends extend this to truncate tables
+    # or otherwise clean up state between examples.
+  end
+
+  define_method(:drain) do
+    case adapter
+    when :test
+      perform_enqueued_jobs
+    else
+      raise NotImplementedError, "active_job backend harness has no drain strategy for adapter: #{adapter.inspect}"
+    end
+  end
+end

sentry-rails/spec/active_job/support/jobs.rb

@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+require "active_job/railtie"
+
+module Sentry
+  module Specs
+    module ActiveJob
+      class FailingJob < ::ActiveJob::Base
+        self.logger = nil
+
+        class Boom < RuntimeError
+        end
+
+        def perform
+          raise Boom, "Boom!"
+        end
+      end
+    end
+  end
+end

sentry-rails/spec/spec_helper.rb

@@ -27,6 +27,8 @@
 end
 
 Dir["#{__dir__}/support/**/*.rb"].each { |file| require file }
+Dir["#{__dir__}/active_job/support/**/*.rb"].each { |file| require file }
+Dir["#{__dir__}/active_job/shared_examples/**/*.rb"].each { |file| require file }
 
 RAILS_VERSION = Rails.version.to_f