Add a test for the python/exec payload

Author: zeroSteiner

modules/payloads/singles/python/exec.rb

@@ -1,5 +1,5 @@
 module MetasploitModule
-  CachedSize = :dynamic
+  CachedSize = 248
 
   include Msf::Payload::Single
   include Msf::Payload::Python

spec/modules/payloads_spec.rb

@@ -2853,6 +2853,16 @@
                           reference_name: 'php/shell_findsock'
   end
 
+  context 'python/exec' do
+    it_should_behave_like 'payload cached size is consistent',
+                          ancestor_reference_names: [
+                              'singles/python/exec'
+                          ],
+                          dynamic_size: false,
+                          modules_pathname: modules_pathname,
+                          reference_name: 'python/exec'
+  end
+
   context 'python/meterpreter/bind_tcp' do
     it_should_behave_like 'payload cached size is consistent',
                           ancestor_reference_names: [