Adding a check to see if the config file exists, if not then return an empty list so we get the would be changes. Adding a test for this functionality.

salt/modules/linux_sysctl.py

@@ -71,6 +71,10 @@ def show(config_file=False):
     '''
     ret = {}
     if config_file:
+        # If the file doesn't exist, return an empty list
+        if not os.path.exists(config_file):
+            return []
+
         try:
             with salt.utils.files.fopen(config_file) as fp_:
                 for line in fp_:

salt/states/sysctl.py

@@ -62,7 +62,7 @@ def present(name, value, config=None):
     if __opts__['test']:
         current = __salt__['sysctl.show']()
         configured = __salt__['sysctl.show'](config_file=config)
-        if not configured:
+        if configured is None:
             ret['result'] = None
             ret['comment'] = (
                 'Sysctl option {0} might be changed, we failed to check '

tests/unit/states/test_sysctl.py

@@ -46,6 +46,9 @@ class SysctlTestCase(TestCase, LoaderModuleMockMixin):
 
         ret = {'name': name, 'result': None, 'changes': {}, 'comment': comment}
 
+        comment_empty = ('Sysctl option {0} would be changed to {1}'
+                         ''.format(name, value))
+
         comment1 = ('Sysctl option {0} set to be changed to {1}'
                     .format(name, value))
 
@@ -91,10 +94,15 @@ class SysctlTestCase(TestCase, LoaderModuleMockMixin):
             return [name]
 
         with patch.dict(sysctl.__opts__, {'test': True}):
-            mock = MagicMock(return_value=False)
+            mock = MagicMock(return_value=None)
             with patch.dict(sysctl.__salt__, {'sysctl.show': mock}):
                 self.assertDictEqual(sysctl.present(name, value), ret)
 
+            mock = MagicMock(return_value=[])
+            with patch.dict(sysctl.__salt__, {'sysctl.show': mock}):
+                ret.update({'comment': comment_empty})
+                self.assertDictEqual(sysctl.present(name, value), ret)
+
             with patch.dict(sysctl.__salt__, {'sysctl.show': mock_current}):
                 ret.update({'comment': comment1})
                 self.assertDictEqual(sysctl.present(name, value), ret)