diff --git a/testing/web-platform/tests/feature-policy/policy-extends-to-sandbox.html b/testing/web-platform/tests/feature-policy/policy-extends-to-sandbox.html
new file mode 100644
index 0000000000000..bf5e1a3c57635
--- /dev/null
+++ b/testing/web-platform/tests/feature-policy/policy-extends-to-sandbox.html
@@ -0,0 +1,241 @@
+<
+!
+DOCTYPE
+html
+>
+<
+title
+>
+Feature
+policy
+treats
+opaque
+origins
+correctly
+<
+/
+title
+>
+<
+script
+src
+=
+"
+/
+resources
+/
+testharness
+.
+js
+"
+>
+<
+/
+script
+>
+<
+script
+src
+=
+"
+/
+resources
+/
+testharnessreport
+.
+js
+"
+>
+<
+/
+script
+>
+<
+body
+>
+<
+script
+>
+"
+use
+strict
+"
+;
+async_test
+(
+t
+=
+>
+{
+let
+frame
+=
+document
+.
+createElement
+(
+'
+iframe
+'
+)
+;
+frame
+.
+src
+=
+"
+/
+feature
+-
+policy
+/
+resources
+/
+sandbox
+-
+self
+.
+html
+"
+;
+frame
+.
+allow
+=
+"
+fullscreen
+"
+;
+frame
+.
+sandbox
+=
+"
+allow
+-
+scripts
+"
+;
+var
+handle_message
+=
+t
+.
+step_func
+(
+evt
+=
+>
+{
+if
+(
+evt
+.
+source
+=
+=
+=
+frame
+.
+contentWindow
+)
+{
+assert_equals
+(
+evt
+.
+data
+.
+child
+true
+"
+'
+self
+'
+in
+header
+should
+match
+origin
+of
+sandboxed
+frame
+.
+"
+)
+;
+assert_equals
+(
+evt
+.
+data
+.
+grandchild
+false
+"
+Opaque
+origins
+should
+not
+match
+each
+other
+.
+"
+)
+;
+document
+.
+body
+.
+removeChild
+(
+frame
+)
+;
+window
+.
+removeEventListener
+(
+'
+message
+'
+handle_message
+)
+;
+t
+.
+done
+(
+)
+;
+}
+}
+)
+;
+window
+.
+addEventListener
+(
+'
+message
+'
+handle_message
+)
+;
+document
+.
+body
+.
+appendChild
+(
+frame
+)
+;
+}
+)
+;
+<
+/
+script
+>
diff --git a/testing/web-platform/tests/feature-policy/resources/nested-sandbox.html b/testing/web-platform/tests/feature-policy/resources/nested-sandbox.html
new file mode 100644
index 0000000000000..0d76654dab162
--- /dev/null
+++ b/testing/web-platform/tests/feature-policy/resources/nested-sandbox.html
@@ -0,0 +1,65 @@
+<
+!
+DOCTYPE
+html
+>
+<
+title
+>
+Return
+fullscreen
+feature
+policy
+state
+<
+/
+title
+>
+<
+script
+>
+"
+use
+strict
+"
+;
+window
+.
+onload
+=
+(
+)
+=
+>
+{
+window
+.
+parent
+.
+postMessage
+(
+document
+.
+featurePolicy
+.
+allowedFeatures
+(
+)
+.
+includes
+(
+"
+fullscreen
+"
+)
+"
+*
+"
+)
+;
+}
+;
+<
+/
+script
+>
diff --git a/testing/web-platform/tests/feature-policy/resources/sandbox-self.html b/testing/web-platform/tests/feature-policy/resources/sandbox-self.html
new file mode 100644
index 0000000000000..4bc7ddd14ca08
--- /dev/null
+++ b/testing/web-platform/tests/feature-policy/resources/sandbox-self.html
@@ -0,0 +1,187 @@
+<
+!
+DOCTYPE
+html
+>
+<
+title
+>
+Return
+fullscreen
+feature
+policy
+state
+from
+self
+and
+a
+sandboxed
+child
+frame
+<
+/
+title
+>
+<
+script
+>
+"
+use
+strict
+"
+;
+window
+.
+onload
+=
+(
+)
+=
+>
+{
+let
+frame
+=
+document
+.
+createElement
+(
+'
+iframe
+'
+)
+;
+frame
+.
+src
+=
+"
+/
+feature
+-
+policy
+/
+resources
+/
+nested
+-
+sandbox
+.
+html
+"
+;
+frame
+.
+sandbox
+=
+"
+allow
+-
+scripts
+"
+;
+var
+handle_message
+=
+evt
+=
+>
+{
+if
+(
+evt
+.
+source
+=
+=
+=
+frame
+.
+contentWindow
+)
+{
+window
+.
+parent
+.
+postMessage
+(
+{
+"
+child
+"
+:
+document
+.
+featurePolicy
+.
+allowedFeatures
+(
+)
+.
+includes
+(
+"
+fullscreen
+"
+)
+"
+grandchild
+"
+:
+evt
+.
+data
+}
+"
+*
+"
+)
+;
+document
+.
+body
+.
+removeChild
+(
+frame
+)
+;
+window
+.
+removeEventListener
+(
+'
+message
+'
+handle_message
+)
+;
+}
+}
+;
+window
+.
+addEventListener
+(
+'
+message
+'
+handle_message
+)
+;
+document
+.
+body
+.
+appendChild
+(
+frame
+)
+;
+}
+;
+<
+/
+script
+>
diff --git a/testing/web-platform/tests/feature-policy/resources/sandbox-self.html.headers b/testing/web-platform/tests/feature-policy/resources/sandbox-self.html.headers
new file mode 100644
index 0000000000000..107bd4b1898f8
--- /dev/null
+++ b/testing/web-platform/tests/feature-policy/resources/sandbox-self.html.headers
@@ -0,0 +1,8 @@
+Feature
+-
+Policy
+:
+fullscreen
+'
+self
+'