try this warning suppression approach

Author: joelhawksley

lib/view_component/template.rb

@@ -24,7 +24,7 @@ def initialize(component:, details:, path:)
         # If the template file has no format (e.g. .erb instead of .html.erb),
         # assume the default format (html).
         if details.format.nil?
-          Kernel.warn("Template format for #{path} is missing, defaulting to :html.")
+          Kernel.warn("WARNING: Template format for #{path} is missing, defaulting to :html.")
           details = ActionView::TemplateDetails.new(details.locale, details.handler, DEFAULT_FORMAT, details.variant)
         end
 

test/sandbox/config/environments/test.rb

@@ -9,7 +9,6 @@
 end
 
 Warning.ignore(/warning: parser\/current/)
-Warning.ignore(/(format_less_parent|format_less_child|no_format)_component.erb is missing, defaulting to :html/)
 
 Sandbox::Application.configure do
   # Settings specified here will take precedence over those in config/application.rb

test/test_helper.rb

@@ -14,6 +14,7 @@ module Warning
     def self.warn(message)
       called_by = caller_locations(1, 1).first.path
       return super unless called_by&.start_with?(PROJECT_ROOT) && !called_by.start_with?("#{PROJECT_ROOT}/vendor")
+      return super if message.include?("Template format for")
 
       raise "Warning: #{message}"
     end