Verify more constants are not loaded at startup

Loading different constants can be tricky with all the requires in
Homebrew so we want to strengthen the existing checks to make
sure that things are not getting required when there is a performance
penalty. This expands the existing check to include more constants
beyond `Formula` that we don't expect to be defined and that pull
in a lot of other dependencies.

Library/Homebrew/test/global_spec.rb

@@ -1,8 +1,8 @@
 # frozen_string_literal: true
 
 RSpec.describe Homebrew, :integration_test do
-  it "does not invoke `require \"formula\"` at startup" do
-    expect { brew "verify-formula-undefined" }
+  it "does not require slow dependencies at startup" do
+    expect { brew "verify-undefined" }
       .to not_to_output.to_stdout
       .and not_to_output.to_stderr
       .and be_a_success

Library/Homebrew/test/support/helper/cmd/brew-verify-undefined.rb

@@ -0,0 +1,33 @@
+# typed: strict
+# frozen_string_literal: true
+
+require "cli/parser"
+
+UNDEFINED_CONSTANTS = %w[
+  Cask::Cask
+  Formula
+  Formulary
+  Homebrew::API
+  Tap
+].freeze
+
+parser = Homebrew::CLI::Parser.new do
+  usage_banner <<~EOS
+    `verify-undefined`
+
+    Verifies that the following constants have not been defined
+    at startup to make sure that startup times stay consistent.
+
+    Contants:
+    #{UNDEFINED_CONSTANTS.join("\n")}
+  EOS
+end
+
+parser.parse
+
+UNDEFINED_CONSTANTS.each do |constant_name|
+  Object.const_get(constant_name)
+  ofail "#{constant_name} should not be defined at startup"
+rescue NameError
+  # We expect this to error as it should not be defined.
+end