diff --git a/config/environments/test.rb b/config/environments/test.rb
index cfba7d0307..e241e5c4ce 100644
--- a/config/environments/test.rb
+++ b/config/environments/test.rb
@@ -52,7 +52,18 @@ Openfoodnetwork::Application.configure do
   # config.active_record.schema_format = :sql
 
   # Print deprecation notices to the stderr
-  config.active_support.deprecation = :stderr
+  # config.active_support.deprecation = :stderr
+
+  # Fail tests on deprecated code unless it's a known case to solve.
+  ActiveSupport::Deprecation.behavior = ->(message, callstack, deprecation_horizon, gem_name) do
+    allowed_warnings = [
+      # List strings here to allow matching deprecations.
+      "Enumerable.sum", # spec/lib/reports/bulk_coop_report_spec.rb:188
+    ]
+    unless allowed_warnings.any? { |pattern| message.match(pattern) }
+      ActiveSupport::Deprecation::DEFAULT_BEHAVIORS[:raise].call(message, callstack, deprecation_horizon, gem_name)
+    end
+  end
 
   config.active_job.queue_adapter = :test
 end