Add test for $out and $evl variables

Co-authored-by: swissspidy <841956+swissspidy@users.noreply.github.com>

Author: Copilot

features/shell.feature

@@ -95,3 +95,23 @@ Feature: WordPress REPL
       """
       => string(16) "this should work"
       """
+
+  Scenario: User can define variables named $out and $evl
+    Given a WP install
+    And a session file:
+      """
+      $out = 'out should work';
+      $evl = 'evl should work';
+      $out;
+      $evl;
+      """
+
+    When I run `wp shell --basic < session`
+    Then STDOUT should contain:
+      """
+      => string(15) "out should work"
+      """
+    And STDOUT should contain:
+      """
+      => string(15) "evl should work"
+      """