test: cover MailerMessageTest, test_requires_a_from_address

test/test_mailer_preview.rb

@@ -0,0 +1,70 @@
+require 'minitest/autorun'
+require 'prism'
+require 'tmpdir'
+require 'fileutils'
+
+class MailerPreviewTest < Minitest::Test
+  def setup
+    @dir = Dir.mktmpdir('prism-mailer-preview')
+    FileUtils.mkdir_p(File.join(@dir, 'preview_user'))
+    File.write(File.join(@dir, 'preview_user/welcome.text.erb'), "Hi <%= name %>\n")
+
+    mailer_dir = @dir
+    @mailer_class = Class.new(Prism::Mailer::Base) do
+      self.template_roots = [mailer_dir]
+
+      def welcome(name)
+        @name = name
+        mail(to: 'someone@example.com', subject: 'Welcome!')
+      end
+    end
+    Object.const_set(:PreviewUserMailer, @mailer_class)
+
+    mailer_class = @mailer_class
+    @preview_class = Class.new(Prism::Mailer::Preview) do
+      define_method(:welcome) { mailer_class.welcome('Fixture Fred') }
+    end
+    Object.const_set(:UserMailerPreview, @preview_class)
+  end
+
+  def teardown
+    Prism::Mailer::Preview.registry.delete(@preview_class)
+    %i[UserMailerPreview PreviewUserMailer].each do |name|
+      Object.send(:remove_const, name) if Object.const_defined?(name)
+    end
+    FileUtils.remove_entry(@dir)
+  end
+
+  def test_subclassing_registers_the_preview
+    assert_includes Prism::Mailer::Preview.registry, UserMailerPreview
+  end
+
+  def test_preview_name_strips_the_preview_suffix_and_underscores
+    assert_equal 'user_mailer', UserMailerPreview.preview_name
+  end
+
+  def test_emails_lists_the_defined_preview_actions
+    assert_equal ['welcome'], UserMailerPreview.emails
+  end
+
+  def test_call_renders_the_action_and_returns_its_delivery
+    delivery = UserMailerPreview.call(:welcome)
+    assert_equal "Hi Fixture Fred\n", delivery.message.text_body
+  end
+
+  def test_call_never_delivers_the_message
+    Prism::Mailer.deliveries.clear
+    UserMailerPreview.call(:welcome)
+    assert_empty Prism::Mailer.deliveries
+  end
+
+  def test_call_raises_for_an_unknown_email
+    error = assert_raises(ArgumentError) { UserMailerPreview.call(:does_not_exist) }
+    assert_match(/unknown preview/, error.message)
+  end
+
+  def test_find_looks_up_a_registered_preview_by_name
+    assert_equal UserMailerPreview, Prism::Mailer::Preview.find('user_mailer')
+    assert_nil Prism::Mailer::Preview.find('nonexistent')
+  end
+end