test: cover PreviewFixtures and PreviewPost

test/test_integration_preview.rb

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+require 'minitest/autorun'
+require 'prism'
+require 'tmpdir'
+
+# Fixtures built once at file-load time (same shared-once idiom as
+# TransactionalFixtures in test_testing_transactional.rb) instead of the
+# per-test Dir.mktmpdir/FileUtils.remove_entry setup/teardown every other
+# *_orm test file repeats - safe here because `use_transactional_tests`
+# rolls each test's writes back, so nothing needs re-seeding between runs.
+#
+# PreviewApp mirrors PostsController#preview/#update from examples/blog
+# closely enough to exercise the same assign -> valid? -> changes ->
+# restore_attributes sequence, and the same optimistic-locking
+# StaleObjectError path, through a REAL HTTP request cycle - something only
+# ever exercised end-to-end via blog_demo.rb until now. It does not require
+# examples/blog/app.rb itself: that file calls `Prism::Orm.connect` against
+# a real on-disk dev database as a process-wide global, which would leak
+# into every other test in this suite that relies on `Prism::Orm.store`.
+module PreviewFixtures
+  DIR = Dir.mktmpdir('prism-preview-integration')
+  STORE = Prism::Orm::Store.new(File.join(DIR, 'test.pstore'))
+  STORE.create_table(:preview_posts, %w[id title body lock_version])
+
+  class PreviewPost < Prism::Orm::Model
+    self.store = STORE
+    table_name :preview_posts
+    validates :title, presence: true
+  end
+
+  class PreviewApp < Prism::Application
+    get('/posts/:id') do
+      post = PreviewPost.find(params['id'])
+      json(id: post.id, title: post.title, body: post.body, lock_version: post.lock_version)
+    end
+
+    # Same shape as PostsController#preview: dirty-track a proposed edit,
+    # capture the diff and any validation errors, then restore the record
+    # to exactly what was persisted before responding - nothing here ever
+    # calls #save.
+    patch('/posts/:id/preview') do
+      post = PreviewPost.find(params['id'])
+      attempted = params.require('post').permit(:title, :body, :lock_version).to_h
+      post.assign(attempted)
+      post.valid?
+      diff = post.changes.reject { |field, _| field == 'lock_version' }
+      errors = post.errors.full_messages
+      post.restore_attributes
+      json(diff: diff, errors: errors, current_title: post.title, current_body: post.body)
+    end
+
+    patch('/posts/:id') do
+      post = PreviewPost.find(params['id'])
+      post.assign(params.require('post').permit(:title, :body, :lock_version).to_h)
+      begin
+        post.save!
+        json(id: post.id, title: post.title, lock_version: post.lock_version)
+      rescue Prism::Orm::StaleObjectError
+        halt(409, 'stale object')
+      end
+    end
+  end
+end
+
+class IntegrationPreviewTest < Minitest::Test
+  include Prism::Testing::IntegrationTest
+  integration_app PreviewFixtures::PreviewApp
+  use_transactional_tests(store: PreviewFixtures::STORE)
+
+  def test_preview_returns_a_diff_without_persisting_the_change
+    post = PreviewFixtures::PreviewPost.create!(title: 'Original title', body: 'original body')
+
+    patch("/posts/#{post.id}/preview", params: { post: { title: 'Proposed title', body: 'original body' } })
+    assert_response :success
+    body = response.json
+    assert_equal ['Original title', 'Proposed title'], body.dig('diff', 'title')
+    assert_empty body['errors']
+    assert_equal 'Original title', body['current_title'], 'the response must show the record as still unsaved'
+
+    get("/posts/#{post.id}")
+    assert_equal 'Original title', response.json['title'], 'the store itself must be untouched by the preview'
+  end
+
+  def test_preview_reports_validation_errors_without_persisting_anything
+    post = PreviewFixtures::PreviewPost.create!(title: 'Keep me', body: 'keep me too')
+
+    patch("/posts/#{post.id}/preview", params: { post: { title: '', body: 'still keep me too' } })
+    assert_response :success
+    body = response.json
+    refute_empty body['errors']
+    assert_equal 'Keep me', body['current_title']
+
+    get("/posts/#{post.id}")
+    assert_equal 'Keep me', response.json['title']
+  end
+
+  def test_preview_is_unaffected_by_a_stale_lock_version_because_it_never_saves
+    post = PreviewFixtures::PreviewPost.create!(title: 'Racing edit', body: 'body')
+    stale_lock_version = post.lock_version
+    post.update!(body: 'a concurrent edit landed first')
+    refute_equal stale_lock_version, post.lock_version
+
+    patch("/posts/#{post.id}/preview",
+          params: { post: { title: 'Whatever I typed', body: 'body', lock_version: stale_lock_version } })
+    assert_response :success # must not raise StaleObjectError - it only diffs, it never saves
+    assert_equal 'a concurrent edit landed first', response.json['current_body']
+  end
+
+  def test_real_update_with_a_stale_lock_version_is_rejected_with_409
+    post = PreviewFixtures::PreviewPost.create!(title: 'Racing edit', body: 'body')
+    stale_lock_version = post.lock_version
+    post.update!(body: 'a concurrent edit landed first')
+
+    patch("/posts/#{post.id}", params: { post: { title: 'Racing edit', body: 'my edit', lock_version: stale_lock_version } })
+    assert_response 409
+
+    get("/posts/#{post.id}")
+    assert_equal 'a concurrent edit landed first', response.json['body'],
+                 'the losing, stale update must never have been applied'
+  end
+
+  def test_real_update_with_a_fresh_lock_version_succeeds
+    post = PreviewFixtures::PreviewPost.create!(title: 'Racing edit', body: 'body')
+
+    patch("/posts/#{post.id}", params: { post: { title: 'Racing edit', body: 'my edit', lock_version: post.lock_version } })
+    assert_response :success
+    assert_equal 1, response.json['lock_version']
+  end
+end