Update test to simulate missing mysqli extension scenario

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

Author: Copilot

features/core-install.feature

@@ -395,14 +395,26 @@ Feature: Install WordPress core
     When I run `chmod 644 wp-admin/includes/upgrade.php`
     Then the return code should be 0
 
-  Scenario: Core install should provide helpful error when WordPress file has fatal error
+  Scenario: Core install should provide helpful error when WordPress file has fatal error from missing extension
     Given an empty directory
     And WP files
     And wp-config.php
     And a database
 
-    # Inject a fatal error into a WordPress core file that will be loaded during install
-    When I run `echo "<?php trigger_error('Simulated fatal error', E_USER_ERROR);" > wp-admin/includes/upgrade.php`
+    # Simulate a missing mysqli extension by injecting a fatal error that mimics
+    # what happens when mysqli_connect is called but the extension is not available
+    # This reproduces the original bug report scenario
+    When I run `echo "<?php trigger_error('Call to undefined function mysqli_connect()', E_USER_ERROR);" > wp-includes/mysqli-check.php`
+    Then the return code should be 0
+
+    # Inject this check at the beginning of upgrade.php to trigger the error during install
+    When I run `echo "<?php require_once ABSPATH . 'wp-includes/mysqli-check.php';" > wp-admin/includes/upgrade-new.php`
+    Then the return code should be 0
+
+    When I run `cat wp-admin/includes/upgrade.php >> wp-admin/includes/upgrade-new.php`
+    Then the return code should be 0
+
+    When I run `mv wp-admin/includes/upgrade-new.php wp-admin/includes/upgrade.php`
     Then the return code should be 0
 
     When I try `wp core install --url=example.org --title=Test --admin_user=testadmin --admin_email=testadmin@example.com --admin_password=testpass`
@@ -414,4 +426,8 @@ Feature: Install WordPress core
       """
       This often indicates a missing PHP extension or a corrupted WordPress installation
       """
+    And STDERR should contain:
+      """
+      Call to undefined function mysqli_connect()
+      """
     And the return code should be 1