diff --git a/testing/web-platform/tests/portals/portals-adopt-predecessor.html b/testing/web-platform/tests/portals/portals-adopt-predecessor.html
index 91c13277819e..e75c3b59424c 100644
--- a/testing/web-platform/tests/portals/portals-adopt-predecessor.html
+++ b/testing/web-platform/tests/portals/portals-adopt-predecessor.html
@@ -35,4 +35,21 @@
     });
     window.open(`resources/portals-adopt-predecessor.html?test=${test}`);
   }, "Tests that trying to adopt the predecessor after the PortalActivateEvent will throw an exception.");
+
+  promise_test(async t => {
+    var test = "adopt-and-activate";
+    window.open(`resources/portals-adopt-predecessor.html?test=${test}`);
+    var message = await waitForCompletion(test);
+    assert_equals(message, "passed");
+  }, "Tests that activating an adopted predecessor without inserting it works");
+
+  async_test(t => {
+    var test = "adopt-attach-remove";
+    var bc = new BroadcastChannel(`test-${test}`);
+    bc.onmessage = t.step_func_done(function(e) {
+      assert_equals(e.data, "passed");
+      bc.close();
+    });
+    window.open(`resources/portals-adopt-predecessor.html?test=${test}`);
+  }, "Tests that an adopting, inserting and then removing a predecessor works correctly");
 </script>
diff --git a/testing/web-platform/tests/portals/resources/portals-adopt-predecessor-portal.html b/testing/web-platform/tests/portals/resources/portals-adopt-predecessor-portal.html
index 78c6af1268cb..0cf07f3f41c1 100644
--- a/testing/web-platform/tests/portals/resources/portals-adopt-predecessor-portal.html
+++ b/testing/web-platform/tests/portals/resources/portals-adopt-predecessor-portal.html
@@ -37,5 +37,19 @@
         }
       });
     }
+    if (test == "adopt-and-activate") {
+      var portal = e.adoptPredecessor();
+      portal.activate();
+    }
+    if (test == "adopt-attach-remove") {
+      var portal = e.adoptPredecessor();
+      document.body.appendChild(portal);
+      setTimeout(() => {
+        document.body.removeChild(portal);
+        var bc_test = new BroadcastChannel(`test-${test}`);
+        bc_test.postMessage("passed");
+        bc_test.close();
+      });
+    }
   }
 </script>
diff --git a/testing/web-platform/tests/portals/resources/portals-adopt-predecessor.html b/testing/web-platform/tests/portals/resources/portals-adopt-predecessor.html
index 4bd01c338ed6..66d47d12ac28 100644
--- a/testing/web-platform/tests/portals/resources/portals-adopt-predecessor.html
+++ b/testing/web-platform/tests/portals/resources/portals-adopt-predecessor.html
@@ -8,6 +8,9 @@
   portal.src = `portals-adopt-predecessor-portal.html?test=${test}`;
   portal.onload = () => {
     portal.activate().then(() => {
+      window.addEventListener("portalactivate", e => {
+        window.opener.postMessage({test, message: "passed"}, "*");
+      });
       window.portalHost.addEventListener("message", e => {
         window.opener.postMessage({test, message: e.data}, "*");
       });