diff --git a/test/ruby/test_exception.rb b/test/ruby/test_exception.rb
index 0a0af390ca..ffa7aa6703 100644
--- a/test/ruby/test_exception.rb
+++ b/test/ruby/test_exception.rb
@@ -1421,4 +1421,33 @@ $stderr = $stdout; raise "\x82\xa0"') do |outs, errs, status|
       end
     end;
   end
+
+  def test_detailed_message
+    e = RuntimeError.new("message")
+    assert_equal("message (RuntimeError)", e.detailed_message)
+    assert_equal("\e[1mmessage (\e[1;4mRuntimeError\e[m\e[1m)\e[m", e.detailed_message(highlight: true))
+
+    e = RuntimeError.new("foo\nbar\nbaz")
+    assert_equal("foo (RuntimeError)\nbar\nbaz", e.detailed_message)
+    assert_equal("\e[1mfoo (\e[1;4mRuntimeError\e[m\e[1m)\e[m\n\e[1mbar\e[m\n\e[1mbaz\e[m", e.detailed_message(highlight: true))
+
+    e = RuntimeError.new("")
+    assert_equal("unhandled exception", e.detailed_message)
+    assert_equal("\e[1;4munhandled exception\e[m", e.detailed_message(highlight: true))
+
+    e = RuntimeError.new
+    assert_equal("RuntimeError (RuntimeError)", e.detailed_message)
+    assert_equal("\e[1mRuntimeError (\e[1;4mRuntimeError\e[m\e[1m)\e[m", e.detailed_message(highlight: true))
+  end
+
+  def test_full_message_with_custom_detailed_message
+    e = RuntimeError.new("message")
+    opt_ = nil
+    e.define_singleton_method(:detailed_message) do |**opt|
+      opt_ = opt
+      "BOO!"
+    end
+    assert_match("BOO!", e.full_message.lines.first)
+    assert_equal({ highlight: Exception.to_tty? }, opt_)
+  end
 end