Added test command caching and refactored inspec helper to run_cmd.

Helps with some of the tests that want to run ruby directly.

Fixes #4416.

test/functional/helper.rb

@@ -107,21 +107,47 @@ module FunctionalHelper
     _(failed_tests).must_be_empty
   end
 
-  def inspec(commandline, prefix = nil)
-    if is_windows?
-      invocation = "/windows/system32/cmd /C \"#{prefix} #{exec_inspec} #{commandline}\""
-      result = CMD.run_command(invocation)
-      result.stdout.encode!(universal_newline: true)
-      result.stderr.encode!(universal_newline: true)
-      convert_windows_output(result.stdout)
-      # remove the CLIXML header trash in windows
-      result.stderr.gsub!("#< CLIXML\n", "")
-    else
-      invocation = "#{prefix} #{exec_inspec} #{commandline}"
-      result = CMD.run_command(invocation)
-    end
+  @inspec_mutex ||= Mutex.new
 
-    result
+  def self.inspec_mutex
+    @inspec_mutex
+  end
+
+  def self.inspec_cache
+    @inspec_cache ||= {}
+  end
+
+  def inspec_cache
+    FunctionalHelper.inspec_cache
+  end
+
+  def inspec_mutex
+    FunctionalHelper.inspec_mutex
+  end
+
+  def run_cmd(commandline, prefix = nil)
+    inspec_mutex.synchronize { # rubocop:disable Style/BlockDelimiters
+      inspec_cache[[commandline, prefix]] ||=
+        if is_windows?
+          invocation = "/windows/system32/cmd /C \"#{prefix} #{commandline}\""
+          # puts
+          # puts "CMD = #{invocation}"
+          result = CMD.run_command(invocation)
+          result.stdout.encode!(universal_newline: true)
+          result.stderr.encode!(universal_newline: true)
+          convert_windows_output(result.stdout)
+          # remove the CLIXML header trash in windows
+          result.stderr.gsub!("#< CLIXML\n", "")
+          result
+        else
+          invocation = "#{prefix} #{commandline}"
+          CMD.run_command(invocation)
+        end
+    }
+  end
+
+  def inspec(commandline, prefix = nil)
+    run_cmd "#{exec_inspec} #{commandline}", prefix
   end
 
   def inspec_with_env(commandline, env = {})