Add testing code for calling #detailed_message

test/test_rake_application.rb

@@ -60,6 +60,33 @@ def test_display_exception_details
     assert_match __method__.to_s, err
   end
 
+  if Exception.method_defined?(:detailed_message)
+    def test_display_exception_details_with_detailed_message
+      error_class = Class.new(StandardError) do
+        def detailed_message(**)
+          "detailed_message!!"
+        end
+      end
+
+      begin
+        raise error_class
+      rescue error_class => ex
+      end
+
+      out, err = capture_io do
+        @app.set_default_options # reset trace output IO
+
+        @app.display_error_message ex
+      end
+
+      assert_empty out
+
+      assert_match "rake aborted!", err
+      assert_match "detailed_message!!", err
+      assert_match __method__.to_s, err
+    end
+  end
+
   def test_display_exception_details_bad_encoding
     begin
       raise "El Niño is coming!".dup.force_encoding("US-ASCII")