Fail before suite if more than 1 thread exists

MSP-11147

Detect thread leaks in a `before(:suite)` configured by
`Metasploit::Framework::Spec::Threads::Suite.configure!` and fail if any
leaks are found.

lib/metasploit/framework.rb

@@ -32,6 +32,10 @@ module Metasploit
   # works in compatible manner with activerecord's rake tasks and other
   # railties.
   module Framework
+    extend ActiveSupport::Autoload
+
+    autoload :Spec
+
     # Returns the root of the metasploit-framework project.  Use in place of
     # `Rails.root`.
     #

lib/metasploit/framework/spec.rb

@@ -0,0 +1,5 @@
+module Metasploit::Framework::Spec
+  extend ActiveSupport::Autoload
+
+  autoload :Threads
+end

lib/metasploit/framework/spec/threads.rb

@@ -0,0 +1,5 @@
+module Metasploit::Framework::Spec::Threads
+  extend ActiveSupport::Autoload
+
+  autoload :Suite
+end

lib/metasploit/framework/spec/threads/suite.rb

@@ -0,0 +1,35 @@
+module Metasploit::Framework::Spec::Threads::Suite
+  #
+  # CONSTANTS
+  #
+
+  EXPECTED_THREAD_COUNT_BEFORE_SUITE = 1
+
+  #
+  # Module Methods
+  #
+
+  # Configures `before(:suite)` and `after(:suite)` callback to detect thread leaks.
+  #
+  # @return [void]
+  def self.configure!
+    unless @configured
+      RSpec.configure do |config|
+        config.before(:suite) do
+          thread_count = Thread.list.count
+
+          expect(thread_count).to(
+              (be <= EXPECTED_THREAD_COUNT_BEFORE_SUITE),
+              "#{thread_count} #{'thread'.pluralize(thread_count)} exist(s) when " \
+              "only #{EXPECTED_THREAD_COUNT_BEFORE_SUITE} #{'thread'.pluralize(EXPECTED_THREAD_COUNT_BEFORE_SUITE)} " \
+              "expected before suite runs"
+          )
+        end
+      end
+
+      @configured = true
+    end
+
+    @configured
+  end
+end

spec/spec_helper.rb

@@ -55,3 +55,5 @@ RSpec.configure do |config|
   # instead of true.
   config.use_transactional_fixtures = true
 end
+
+Metasploit::Framework::Spec::Threads::Suite.configure!