MDL-49687 enrol: Add behat tests for adding multiple groups

enrol/tests/behat/add_to_group.feature

+@core_enrol @core_group
+Feature: Users can be added to multiple groups at once
+  In order to manage group membership effectively
+  As a user
+  I need to add another user to multiple groups
+
+  Background:
+    Given the following "users" exist:
+      | username | firstname | lastname | email |
+      | teacher1 | Teacher | 1 | teacher1@asd.com |
+      | student1 | Student | 1 | student1@asd.com |
+    And the following "courses" exist:
+      | fullname | shortname | format |
+      | Course 1 | C1 | topics |
+    And the following "groups" exist:
+      | name | course | idnumber |
+      | Group 1 | C1 | G1 |
+      | Group 2 | C1 | G2 |
+      | Group 3 | C1 | G3 |
+    And the following "course enrolments" exist:
+      | user | course | role |
+      | teacher1 | C1 | editingteacher |
+      | student1 | C1 | editingteacher |
+
+  Scenario: Adding a user to one group
+    Given I log in as "teacher1"
+    And I follow "Course 1"
+    And I navigate to "Enrolled users" node in "Course administration > Users"
+    And I click on "Add user into group" "link" in the "student1" "table_row"
+    When I set the field "Add user into group" to "Group 1"
+    And I press "Save changes"
+    Then I should see "Group 1"
+
+  Scenario: Adding a user to multiple group
+    Given I log in as "teacher1"
+    And I follow "Course 1"
+    And I navigate to "Enrolled users" node in "Course administration > Users"
+    And I click on "Add user into group" "link" in the "student1" "table_row"
+    When I set the field "Add user into group" to "Group 1, Group 2, Group 3"
+    And I press "Save changes"
+    Then I should see "Group 1"
+    And I should see "Group 2"
+    And I should see "Group 3"