diff --git a/actionmailer/lib/action_mailer/test_case.rb b/actionmailer/lib/action_mailer/test_case.rb
index 63e18147f6..c4de029694 100644
--- a/actionmailer/lib/action_mailer/test_case.rb
+++ b/actionmailer/lib/action_mailer/test_case.rb
@@ -17,7 +17,14 @@ module ActionMailer
 
       module ClassMethods
         def tests(mailer)
-          self._mailer_class = mailer
+          case mailer
+          when String, Symbol
+            self._mailer_class = mailer.to_s.camelize.constantize
+          when Module
+            self._mailer_class = mailer
+          else
+            raise NonInferrableMailerError.new(mailer)
+          end
         end
 
         def mailer_class
diff --git a/actionmailer/test/test_test.rb b/actionmailer/test/test_test.rb
new file mode 100644
index 0000000000..86fd37bea6
--- /dev/null
+++ b/actionmailer/test/test_test.rb
@@ -0,0 +1,28 @@
+require 'abstract_unit'
+
+class TestTestMailer < ActionMailer::Base
+end
+
+class CrazyNameMailerTest < ActionMailer::TestCase
+  tests TestTestMailer
+
+  def test_set_mailer_class_manual
+    assert_equal TestTestMailer, self.class.mailer_class
+  end
+end
+
+class CrazySymbolNameMailerTest < ActionMailer::TestCase
+  tests :test_test_mailer
+
+  def test_set_mailer_class_manual_using_symbol
+    assert_equal TestTestMailer, self.class.mailer_class
+  end
+end
+
+class CrazyStringNameMailerTest < ActionMailer::TestCase
+  tests 'test_test_mailer'
+
+  def test_set_mailer_class_manual_using_string
+    assert_equal TestTestMailer, self.class.mailer_class
+  end
+end