Scrollable modal (#27769)

js/tests/unit/modal.js

@@ -790,4 +790,31 @@ $(function () {
     })
       .bootstrapModal('show')
   })
+
+  QUnit.test('should scroll to top of the modal body if the modal has .modal-dialog-scrollable class', function (assert) {
+    assert.expect(2)
+    var done = assert.async()
+
+    var $modal = $([
+      '<div id="modal-test">',
+      '  <div class="modal-dialog modal-dialog-scrollable">',
+      '    <div class="modal-content">',
+      '      <div class="modal-body" style="height: 100px; overflow-y: auto;">',
+      '        <div style="height: 200px" />',
+      '      </div>',
+      '    </div>',
+      '  </div>',
+      '</div>'
+    ].join('')).appendTo('#qunit-fixture')
+
+    var $modalBody = $('.modal-body')
+    $modalBody.scrollTop(100)
+    assert.strictEqual($modalBody.scrollTop(), 100)
+
+    $modal.on('shown.bs.modal', function () {
+      assert.strictEqual($modalBody.scrollTop(), 0, 'modal body scrollTop should be 0 when opened')
+      done()
+    })
+      .bootstrapModal('show')
+  })
 })