diff --git a/testing/web-platform/tests/custom-elements/form-associated/ElementInternals-accessibility.html b/testing/web-platform/tests/custom-elements/form-associated/ElementInternals-accessibility.html
new file mode 100644
index 0000000000000..9574d504666e9
--- /dev/null
+++ b/testing/web-platform/tests/custom-elements/form-associated/ElementInternals-accessibility.html
@@ -0,0 +1,322 @@
+<
+!
+DOCTYPE
+HTML
+>
+<
+script
+src
+=
+"
+/
+resources
+/
+testharness
+.
+js
+"
+>
+<
+/
+script
+>
+<
+script
+src
+=
+"
+/
+resources
+/
+testharnessreport
+.
+js
+"
+>
+<
+/
+script
+>
+<
+script
+>
+class
+TestElement
+extends
+HTMLElement
+{
+constructor
+(
+)
+{
+super
+(
+)
+;
+this
+.
+_internals
+=
+this
+.
+attachInternals
+(
+)
+;
+}
+get
+internals
+(
+)
+{
+return
+this
+.
+_internals
+;
+}
+set
+internals
+(
+val
+)
+{
+throw
+"
+Can
+'
+t
+set
+internals
+!
+"
+;
+}
+}
+customElements
+.
+define
+(
+"
+test
+-
+element
+"
+TestElement
+)
+;
+<
+/
+script
+>
+<
+test
+-
+element
+id
+=
+"
+testElement
+"
+>
+<
+/
+test
+-
+element
+>
+<
+script
+>
+const
+element
+=
+document
+.
+getElementById
+(
+"
+testElement
+"
+)
+;
+const
+properties
+=
+[
+"
+role
+"
+"
+ariaActiveDescendant
+"
+"
+ariaAtomic
+"
+"
+ariaAutoComplete
+"
+"
+ariaBusy
+"
+"
+ariaChecked
+"
+"
+ariaColCount
+"
+"
+ariaColIndex
+"
+"
+ariaColSpan
+"
+"
+ariaControls
+"
+"
+ariaCurrent
+"
+"
+ariaDescribedBy
+"
+"
+ariaDetails
+"
+"
+ariaDisabled
+"
+"
+ariaErrorMessage
+"
+"
+ariaExpanded
+"
+"
+ariaFlowTo
+"
+"
+ariaHasPopup
+"
+"
+ariaHidden
+"
+"
+ariaKeyShortcuts
+"
+"
+ariaLabel
+"
+"
+ariaLabelledBy
+"
+"
+ariaLevel
+"
+"
+ariaLive
+"
+"
+ariaModal
+"
+"
+ariaMultiLine
+"
+"
+ariaMultiSelectable
+"
+"
+ariaOrientation
+"
+"
+ariaOwns
+"
+"
+ariaPlaceholder
+"
+"
+ariaPosInSet
+"
+"
+ariaPressed
+"
+"
+ariaReadOnly
+"
+"
+ariaRelevant
+"
+"
+ariaRequired
+"
+"
+ariaRoleDescription
+"
+"
+ariaRowCount
+"
+"
+ariaRowIndex
+"
+"
+ariaRowSpan
+"
+"
+ariaSelected
+"
+"
+ariaSort
+"
+"
+ariaValueMax
+"
+"
+ariaValueMin
+"
+"
+ariaValueNow
+"
+"
+ariaValueText
+"
+]
+;
+for
+(
+const
+property
+of
+properties
+)
+{
+test
+(
+(
+)
+=
+>
+{
+assert_inherits
+(
+element
+.
+internals
+property
+)
+;
+}
+property
++
+"
+is
+defined
+in
+ElementInternals
+"
+)
+;
+}
+<
+/
+script
+>