Do not mock on nil.

[#47979793]

Using `should_not_receive` on `nil` gives `nil` a permanent
`@mock_proxy`, which causes Marshal.dump to fail in later tests (see
https://travis-ci.org/rapid7/metasploit-framework/builds/6502350).  By,
checking there are no NoMethoErrors raised, nil can be tested as
parent_module, but works around the RSpec issue
(rspec/rspec-mocks#274).

Author: limhoff-r7

spec/lib/msf/core/modules/loader/base_spec.rb

@@ -1168,11 +1168,11 @@ class Metasploit3
 			it 'should do nothing if parent_module is nil' do
 				parent_module = nil
 
-				allow_message_expectations_on_nil
-				parent_module.should_not_receive(:remove_const)
-				parent_module.should_not_receive(:const_set)
-
-				subject.send(:restore_namespace_module, parent_module, relative_name, @original_namespace_module)
+				# can check that NoMethodError is not raised because *const* methods are
+				# not defined on `nil`.
+				expect {
+					subject.send(:restore_namespace_module, parent_module, relative_name, @original_namespace_module)
+				}.to_not raise_error(NoMethodError)
 			end
 
 			context 'with namespace_module nil' do