MDL-70829 course: Mark up decorative images properly

* Decorative images should have an empty alt text and there's no need
to set a presentation role.
* Accessibility Behat tests added to cover the changes:
  - block_starredcourses uses the core_course/no-courses template
  - core_completion tests changes in core_course/activity instance and
    core_course/editdefaultcompletion

blocks/starredcourses/tests/behat/starred_courses.feature

@@ -0,0 +1,42 @@
+@block_starredcourses
+Feature: Starred courses
+  In order for me to quickly navigate to my favourite courses
+  As a user
+  I must be able to add them to the Starred courses block
+
+  Background:
+    Given the following "users" exist:
+      | username | firstname | lastname | email |
+      | student1 | Student | 1 | student1@example.com |
+    And the following "courses" exist:
+      | shortname | fullname |
+      | C1        | Course 1 |
+      | C2        | Course 2 |
+      | C3        | Course 3 |
+    And the following "course enrolments" exist:
+      | user      | course | role    |
+      | student1  | C1     | student |
+      | student1  | C2     | student |
+      | student1  | C3     | student |
+    And the following "blocks" exist:
+      | blockname       | contextlevel | reference | pagetypepattern | defaultregion  |
+      | starredcourses  | User         | student1  | my-index        | content        |
+
+  @accessibility @javascript
+  Scenario: User has no starred courses
+    Given I log in as "student1"
+    Then I should see "No starred courses"
+    And the page should meet accessibility standards
+
+  @accessibility @javascript
+  Scenario: User has starred courses
+    Given I am on the "My courses" page logged in as "student1"
+    And I click on "Actions for course Course 1" "button"
+    And I click on "Star for Course 1" "link"
+    And I click on "Actions for course Course 3" "button"
+    And I click on "Star for Course 3" "link"
+    When I follow "Dashboard"
+    Then the page should meet accessibility standards
+    And I should see "Course 1" in the "Starred courses" "block"
+    And I should see "Course 3" in the "Starred courses" "block"
+    But I should not see "Course 2" in the "Starred courses" "block"

completion/tests/behat/bulk_edit_activity_completion.feature

@@ -78,3 +78,10 @@ Feature: Allow teachers to bulk edit activity completion rules in a course.
     And I should see "With conditions" in the "//div[contains(concat(' ', normalize-space(@class), ' '), ' row ')][.//*[text() = 'Test assignment two']]" "xpath_element"
     And I should see "Passing grade" in the "//div[contains(concat(' ', normalize-space(@class), ' '), ' row ')][.//*[text() = 'Test assignment two']]" "xpath_element"
     And I should not see "Completion expected on" in the "//div[contains(concat(' ', normalize-space(@class), ' '), ' row ')][.//*[text() = 'Test assignment two']]" "xpath_element"
+
+  @accessibility
+  Scenario: Evaluate the accessibility of the bulk edit activity completion page
+    Given I am on the "Course 1" course page logged in as "teacher1"
+    When I navigate to "Course completion" in current page administration
+    And I set the field "Course completion tertiary navigation" to "Bulk edit activity completion"
+    And the page should meet accessibility standards

completion/tests/behat/default_activity_completion.feature

@@ -228,3 +228,10 @@ Feature: Allow teachers to edit the default activity completion rules in a cours
     When I navigate to "Course completion" in current page administration
     And I set the field "Course completion tertiary navigation" to "Default activity completion"
     Then "Quiz" "text" should appear before "Text and media area" "text"
+
+  @accessibility
+  Scenario: Evaluate the accessibility of the default activity completion page
+    Given I am on the "Course 1" course page logged in as "teacher1"
+    When I navigate to "Course completion" in current page administration
+    And I set the field "Course completion tertiary navigation" to "Default activity completion"
+    And the page should meet accessibility standards

course/renderer.php

@@ -378,7 +378,7 @@ class core_course_renderer extends plugin_renderer_base {
 
         $altname = get_accesshide(' ' . $cm->modfullname);
         $name = html_writer::empty_tag('img', array('src' => $cm->get_icon_url(),
-                'class' => 'iconlarge activityicon', 'alt' => ' ', 'role' => 'presentation')) .
+                'class' => 'iconlarge activityicon', 'alt' => '')) .
             html_writer::tag('span', ' '.$cm->get_formatted_name() . $altname, array('class' => 'instancename'));
         $formattedinfo = \core_availability\info::format_info($cm->availableinfo, $cm->get_course());
         return html_writer::div($name, 'activityinstance-error') .

course/templates/activityinstance.mustache

@@ -42,7 +42,7 @@
             <input type="checkbox" id="selectactivity_{{cmid}}" class="mr-1" name="cmid[]" data-section="{{sectionnumber}}" value="{{cmid}}" aria-label="{{#str}}checkactivity, completion, {{{modname}}}{{/str}}">
             {{/canmanage}}
             <a href="{{url}}">
-            <img src="{{icon}}" class="iconlarge activityicon" alt=" " role="presentation" />
+            <img src="{{icon}}" class="iconlarge activityicon" alt="">
             <span class="instancename">{{{modname}}}</span>
             </a>
         </div>

course/templates/editdefaultcompletion.mustache

@@ -38,7 +38,7 @@
         <div class="row mb-1">
             {{#modules}}
                 <div class="col-sm-2">
-                    <img src="{{icon}}" class="mr-1 mb-1" alt=" " role="presentation" />
+                    <img src="{{icon}}" class="mr-1 mb-1" alt="">
                     <span>{{{formattedname}}}</span>
                 </div>
             {{/modules}}

course/templates/no-courses.mustache

@@ -28,10 +28,9 @@
 <div class="text-xs-center text-center mt-3" data-region="empty-message">
     <img class="empty-placeholder-image-lg mt-1"
          src="{{nocoursesimg}}"
-         alt="{{$nocoursestring}}{{#str}} nocourses, core {{/str}}{{/nocoursestring}}"
-         role="presentation">
+         alt="">
     <p class="text-muted mt-3">{{$nocoursestring}}{{#str}} nocourses, core {{/str}}{{/nocoursestring}}</p>
     {{#newcourseurl}}
         <a href="{{{newcourseurl}}}" class="nocourseslink">{{#str}} createnewcourse, core {{/str}}</a>
     {{/newcourseurl}}
-</div>
+</div>