DeprecationToolkit currently can't catch deprecations that are generated before tests are executed

Consider this example of a deprecation warning:
https://github.com/thoughtbot/shoulda-matchers/blob/94b28e4ef4cc001b1c0b4386143b8c05ac163550/lib/shoulda/matchers/warn.rb#L20-L25

A test like this would trigger that deprecation:

class FooModelTest < ActiveSupport::TestCase
  should define_enum_for(:status).with([:pending, :completed, :failed])
end

Here's what gets logged:

************************************************************************
Warning from shoulda-matchers:

The `with` qualifier on `define_enum_for` is deprecated and will be
removed in the next major release. Please use `with_values` instead.
************************************************************************

However, because the deprecated method (with) is called in the code that declares the test cases, not called from within a test, DeprecationToolkit won't catch this deprecation. The deprecation gets logged before attach_subscriber has been invoked.

Is it possible to subscribe to deprecations earlier in the life of the test process?

Start with lib/minitest/deprecation_toolkit_plugin.rb, especially attach_subscriber, and reproduce the FooModelTest example from the issue. Trace when the subscriber is installed relative to test declarations. Done means deprecations emitted before individual tests execute are captured without losing the existing test behavior.