(PUP-11022) Use stub_const/hide_const to define Selinux

Fix order dependent test failures when running spec/unit/util/selinux_spec.rb
followed by spec/unit/transaction_spec.r:b

    Failure/Error: expect(Selinux).to receive(:matchpathcon_fini)
      Selinux does not implement: matchpathcon_fini

stub_const/hide_const automatically restore the previous value when the test
completes.

Author: joshcooper

spec/unit/transaction_spec.rb

@@ -793,16 +793,8 @@ def post_resource_eval
     end
 
     it "should call Selinux.matchpathcon_fini in case Selinux is enabled ", :if => Puppet.features.posix? do
-      unless defined?(Selinux)
-        module Selinux
-          def self.is_selinux_enabled
-            true
-          end
-
-          def self.matchpathcon_fini
-          end
-        end
-      end
+      selinux = double('selinux', is_selinux_enabled: true, matchpathcon_fini: nil)
+      stub_const('Selinux', selinux)
 
       resource = Puppet::Type.type(:file).new(:path => make_absolute("/tmp/foo"))
       transaction = transaction_with_resource(resource)

spec/unit/util/selinux_spec.rb

@@ -3,26 +3,29 @@
 require 'pathname'
 require 'puppet/util/selinux'
 
-unless defined?(Selinux)
-  module Selinux
-    def self.is_selinux_enabled
-      false
-    end
-  end
-end
-
 describe Puppet::Util::SELinux do
   include Puppet::Util::SELinux
 
+  let(:selinux) { double('selinux', is_selinux_enabled: false) }
+
+  before :each do
+    stub_const('Selinux', selinux)
+  end
+
   describe "selinux_support?" do
-    it "should return :true if this system has SELinux enabled" do
+    it "should return true if this system has SELinux enabled" do
       expect(Selinux).to receive(:is_selinux_enabled).and_return(1)
-      expect(selinux_support?).to be_truthy
+      expect(selinux_support?).to eq(true)
     end
 
-    it "should return :false if this system lacks SELinux" do
+    it "should return false if this system has SELinux disabled" do
       expect(Selinux).to receive(:is_selinux_enabled).and_return(0)
-      expect(selinux_support?).to be_falsey
+      expect(selinux_support?).to eq(false)
+    end
+
+    it "should return false if this system lacks SELinux" do
+      hide_const('Selinux')
+      expect(selinux_support?).to eq(false)
     end
 
     it "should return nil if /proc/mounts does not exist" do