MDL-38476 behat: New test

According to MDLQA-9, in a single
simple discussion forum only teachers
can start discussions.

mod/forum/tests/behat/single_forum_discussion.feature

@@ -0,0 +1,43 @@
+@mod_forum
+Feature: Single simple forum discussion type
+  In order to restrict the discussion topic to one
+  As a moodle teacher
+  I need to create a forum with a single simple discussion
+
+  Background:
+    Given the following "users" exists:
+      | username | firstname | lastname | email |
+      | teacher1 | Teacher | 1 | teacher1@asd.com |
+      | student1 | Student | 1 | student1@asd.com |
+    And the following "courses" exists:
+      | fullname | shortname | category |
+      | Course 1 | C1 | 0 |
+    And the following "course enrolments" exists:
+      | user | course | role |
+      | teacher1 | C1 | editingteacher |
+      | student1 | C1 | student |
+    And I log in as "teacher1"
+    And I follow "Course 1"
+    And I turn editing mode on
+    And I add a "forum" to section "1" and I fill the form with:
+      | Forum name | Single discussion forum name |
+      | Forum type | A single simple discussion |
+      | Description | Single discussion forum description |
+
+  @javascript
+  Scenario: Teacher can start the single simple discussion
+    When I follow "Single discussion forum name"
+    Then I should see "Single discussion forum description" in the "div.firstpost.starter" "css_element"
+    And I should not see "Add a new discussion topic"
+
+  @javascript
+  Scenario: Student can not add more discussions
+    Given I log out
+    And I log in as "student1"
+    And I follow "Course 1"
+    When I reply "Single discussion forum name" post from "Single discussion forum name" forum with:
+      | Subject | Reply to single discussion subject |
+      | Message | Reply to single discussion message |
+    Then I should not see "Add a new discussion topic"
+    And I should see "Reply" in the "div.firstpost.starter" "css_element"
+    And I should see "Reply to single discussion message"