diff --git a/testing/web-platform/tests/infrastructure/assumptions/document-fonts-ready.html b/testing/web-platform/tests/infrastructure/assumptions/document-fonts-ready.html
new file mode 100644
index 0000000000000..f581e7b08d604
--- /dev/null
+++ b/testing/web-platform/tests/infrastructure/assumptions/document-fonts-ready.html
@@ -0,0 +1,375 @@
+<
+!
+DOCTYPE
+HTML
+>
+<
+title
+>
+document
+.
+fonts
+.
+ready
+resolves
+after
+layout
+depending
+on
+loaded
+fonts
+<
+/
+title
+>
+<
+link
+rel
+=
+"
+help
+"
+href
+=
+"
+https
+:
+/
+/
+drafts
+.
+csswg
+.
+org
+/
+css
+-
+font
+-
+loading
+/
+#
+fontfaceset
+-
+pending
+-
+on
+-
+the
+-
+environment
+"
+>
+<
+script
+src
+=
+"
+/
+resources
+/
+testharness
+.
+js
+"
+>
+<
+/
+script
+>
+<
+script
+src
+=
+"
+/
+resources
+/
+testharnessreport
+.
+js
+"
+>
+<
+/
+script
+>
+<
+link
+rel
+=
+"
+stylesheet
+"
+type
+=
+"
+text
+/
+css
+"
+href
+=
+"
+/
+fonts
+/
+ahem
+.
+css
+"
+/
+>
+<
+style
+>
+#
+foo
+{
+font
+:
+100px
+/
+1
+Ahem
+;
+}
+<
+/
+style
+>
+<
+div
+id
+=
+"
+log
+"
+>
+<
+/
+div
+>
+<
+span
+id
+=
+"
+foo
+"
+>
+X
+<
+/
+span
+>
+<
+script
+>
+/
+/
+The
+purpose
+of
+this
+test
+is
+to
+ensure
+that
+testharness
+.
+js
+tests
+can
+use
+/
+/
+document
+.
+fonts
+.
+ready
+to
+wait
+for
+a
+web
+font
+to
+load
+without
+having
+to
+/
+/
+wait
+for
+the
+window
+load
+event
+before
+or
+requestAnimationFrame
+after
+.
+/
+/
+/
+/
+The
+spec
+says
+that
+a
+FontFaceSet
+is
+"
+pending
+on
+the
+environment
+"
+if
+"
+the
+/
+/
+document
+has
+pending
+layout
+operations
+which
+might
+cause
+the
+user
+agent
+to
+/
+/
+request
+a
+font
+or
+which
+depend
+on
+recently
+-
+loaded
+fonts
+"
+and
+both
+are
+/
+/
+assumed
+to
+hold
+true
+in
+this
+test
+.
+async_test
+(
+t
+=
+>
+{
+assert_equals
+(
+document
+.
+fonts
+.
+size
+1
+'
+one
+font
+is
+pending
+'
+)
+;
+document
+.
+fonts
+.
+ready
+.
+then
+(
+t
+.
+step_func_done
+(
+(
+)
+=
+>
+{
+const
+span
+=
+document
+.
+getElementById
+(
+'
+foo
+'
+)
+;
+const
+rect
+=
+span
+.
+getBoundingClientRect
+(
+)
+;
+/
+/
+If
+Ahem
+has
+loaded
+the
+X
+will
+be
+100px
+wide
+.
+assert_equals
+(
+rect
+.
+width
+100
+'
+span
+is
+100px
+wide
+'
+)
+;
+}
+)
+)
+;
+}
+)
+;
+<
+/
+script
+>