cachable: make sure to clear caches between tests

This adds a registry for all modules and classes that
cachable is included in. The registry allows us to
programmatically clear all caches in between tests
so that we don't forget to do that when adding a new
class or refactoring code. The goal here is to reduce
the number of flaky tests in the future.

Library/Homebrew/api/cask.rb

@@ -10,9 +10,9 @@ module Homebrew
     #
     # @api private
     module Cask
-      class << self
-        include Cachable
+      extend Cachable
 
+      class << self
         private :cache
 
         sig { params(token: String).returns(Hash) }

Library/Homebrew/api/formula.rb

@@ -10,9 +10,9 @@ module Homebrew
     #
     # @api private
     module Formula
-      class << self
-        include Cachable
+      extend Cachable
 
+      class << self
         private :cache
 
         sig { params(name: String).returns(Hash) }

Library/Homebrew/extend/cachable.rb

@@ -1,4 +1,4 @@
-# typed: strict
+# typed: true
 # frozen_string_literal: true
 
 module Cachable
@@ -11,4 +11,43 @@ module Cachable
   def clear_cache
     cache.clear
   end
+
+  # Collect all classes that mix in Cachable so that those caches can be cleared in-between tests.
+  if ENV["HOMEBREW_TESTS"]
+    def self.included(klass)
+      raise ArgumentError, "Don't use Cachable with singleton classes" if klass.singleton_class?
+
+      super if defined?(super)
+    end
+
+    # Ignore classes that get inherited from a lot and that have
+    # caches that we don't need to clear on the class level.
+    IGNORE_INHERITED_CLASSES = %w[Formula Cask].freeze
+    private_constant :IGNORE_INHERITED_CLASSES
+
+    def self.extended(klass)
+      Registry.list << klass
+      klass.extend(Inherited) unless IGNORE_INHERITED_CLASSES.include?(klass.name)
+      super if defined?(super)
+    end
+
+    module Inherited
+      def inherited(klass)
+        # A class might inherit Cachable at the instance level
+        # and in that case we just want to skip registering it.
+        Registry.list << klass if klass.respond_to?(:clear_cache)
+        super if defined?(super)
+      end
+    end
+
+    module Registry
+      def self.list
+        @list ||= []
+      end
+
+      def self.clear_all_caches
+        list.each(&:clear_cache)
+      end
+    end
+  end
 end

Library/Homebrew/readall.rb

@@ -9,8 +9,9 @@ require "system_command"
 #
 # @api private
 module Readall
+  extend Cachable
+
   class << self
-    include Cachable
     include SystemCommand::Mixin
 
     # TODO: remove this once the `MacOS` module is undefined on Linux

Library/Homebrew/test/spec_helper.rb

@@ -202,16 +202,7 @@ RSpec.configure do |config|
   config.around do |example|
     Homebrew.raise_deprecation_exceptions = true
 
-    Formulary.clear_cache
-    Tap.each(&:clear_cache)
-    Tap.clear_cache
-    DependencyCollector.clear_cache
-    Formula.clear_cache
-    Keg.clear_cache
-    Tab.clear_cache
-    Dependency.clear_cache
-    Requirement.clear_cache
-    Readall.clear_cache if defined?(Readall)
+    Cachable::Registry.clear_all_caches
     FormulaInstaller.clear_attempted
     FormulaInstaller.clear_installed
     FormulaInstaller.clear_fetched
@@ -263,15 +254,7 @@ RSpec.configure do |config|
       @__stderr.close
       @__stdin.close
 
-      Formulary.clear_cache
-      Tap.clear_cache
-      DependencyCollector.clear_cache
-      Formula.clear_cache
-      Keg.clear_cache
-      Tab.clear_cache
-      Dependency.clear_cache
-      Requirement.clear_cache
-      Readall.clear_cache if defined?(Readall)
+      Cachable::Registry.clear_all_caches
 
       FileUtils.rm_rf [
         *TEST_DIRECTORIES,