Bug 1950487 [wpt PR 50945] - DOM: Add slotchange test for moveBefore(), a=testonly

Automatic update from web-platform-tests
DOM: Add slotchange test for moveBefore()

This CL adds a test to ensure that the 'slotchange' event is fired when
slots themselves are moved in and out of a custom element, and their
assigned nodes change.

This addresses
whatwg/dom#1307 (comment).

R=nrosenthal

Bug: 40150299
Change-Id: I93ee04294e5ab3e6d9f75c48705cdc77ce0a1df3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6298941
Commit-Queue: Dominic Farolino <domchromium.org>
Reviewed-by: Noam Rosenthal <nrosenthalchromium.org>
Cr-Commit-Position: refs/heads/main{#1424746}

--

wpt-commits: cd2cfbab2d2157b1c409be1631ff7e42c3ae7f6f
wpt-pr: 50945

UltraBlame original commit: 4a6a1072a3e50a2172f5d712305e8a77f170e452

Author: marco-c

testing/web-platform/tests/dom/nodes/moveBefore/tentative/slotchange-events.html

@@ -946,6 +946,322 @@
 "
 )
 ;
+promise_test
+(
+async
+t
+=
+>
+{
+const
+customElement
+=
+document
+.
+body
+.
+appendChild
+(
+document
+.
+createElement
+(
+'
+custom
+-
+element
+'
+)
+)
+;
+const
+slot
+=
+customElement
+.
+shadowRoot
+.
+children
+[
+0
+]
+;
+t
+.
+add_cleanup
+(
+(
+)
+=
+>
+customElement
+.
+remove
+(
+)
+)
+;
+const
+p
+=
+document
+.
+createElement
+(
+'
+p
+'
+)
+;
+p
+.
+slot
+=
+'
+content
+'
+;
+p
+.
+textContent
+=
+'
+The
+content
+'
+;
+customElement
+.
+appendChild
+(
+p
+)
+;
+/
+/
+See
+the
+above
+tests
+that
+do
+the
+same
+thing
+for
+implementations
+that
+do
+not
+fire
+slotchange
+/
+/
+at
+this
+phase
+.
+await
+new
+Promise
+(
+resolve
+=
+>
+t
+.
+step_timeout
+(
+(
+)
+=
+>
+resolve
+(
+)
+)
+)
+;
+assert_array_equals
+(
+slot
+.
+assignedNodes
+(
+)
+[
+p
+]
+)
+;
+document
+.
+body
+.
+moveBefore
+(
+slot
+null
+)
+;
+await
+new
+Promise
+(
+(
+resolve
+reject
+)
+=
+>
+{
+slot
+.
+addEventListener
+(
+'
+slotchange
+'
+e
+=
+>
+resolve
+(
+)
+{
+once
+:
+true
+}
+)
+;
+t
+.
+step_timeout
+(
+(
+)
+=
+>
+reject
+(
+'
+Timeout
+;
+slotchange
+was
+not
+fired2
+'
+)
+1500
+)
+;
+}
+)
+;
+assert_array_equals
+(
+slot
+.
+assignedNodes
+(
+)
+[
+]
+)
+;
+customElement
+.
+shadowRoot
+.
+moveBefore
+(
+slot
+null
+)
+;
+await
+new
+Promise
+(
+(
+resolve
+reject
+)
+=
+>
+{
+slot
+.
+addEventListener
+(
+'
+slotchange
+'
+e
+=
+>
+resolve
+(
+)
+{
+once
+:
+true
+}
+)
+;
+t
+.
+step_timeout
+(
+(
+)
+=
+>
+reject
+(
+'
+Timeout
+;
+slotchange
+was
+not
+fired3
+'
+)
+1500
+)
+;
+}
+)
+;
+assert_array_equals
+(
+slot
+.
+assignedNodes
+(
+)
+[
+p
+]
+)
+;
+}
+"
+Moving
+a
+slot
+runs
+the
+assign
+slottables
+algorithm
+"
+)
+;
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