ActionMailer::NonInferrableMailerError Ruby on Rails 5.1.2 Class ActionMailer::NonInferrableMailerError < StandardError actionmailer/lib/action_mailer/test_case.rb Methods N new Class Public methods new(name) Link Source: show | on GitHub # File actionmailer/lib/action_mailer/test_case.rb, line 6 def initialize(name) super "Unable to determine the mailer to test from #{name}. " "You'll need to specify it using tests YourMailer in your " "test case definition" end