diff --git a/components/script/dom/webidls/XRTest.webidl b/components/script/dom/webidls/XRTest.webidl
index 6a6b0003eb1..30c485321d4 100644
--- a/components/script/dom/webidls/XRTest.webidl
+++ b/components/script/dom/webidls/XRTest.webidl
@@ -6,9 +6,9 @@
 
 [Exposed=Window, Pref="dom.webxr.test"]
 interface XRTest {
-  // // Simulates connecting a device to the system.
-  // // Used to instantiate a fake device for use in tests.
-  // Promise<FakeXRDeviceController> simulateDeviceConnection(FakeXRDeviceInit);
+  // Simulates connecting a device to the system.
+  // Used to instantiate a fake device for use in tests.
+  Promise<FakeXRDeviceController> simulateDeviceConnection(FakeXRDeviceInit init);
 
   // // Simulates a device being disconnected from the system.
   // Promise<void> simulateDeviceDisconnection(XRDevice);
@@ -18,3 +18,8 @@ interface XRTest {
   // // Device API methods.
   // void simulateUserActivation(Function);
 };
+
+dictionary FakeXRDeviceInit {
+    // TODO: Subject to change to match spec changes.
+    required boolean supportsImmersive;
+};
diff --git a/components/script/dom/xrtest.rs b/components/script/dom/xrtest.rs
index af1d289ae3f..6c895e226cb 100644
--- a/components/script/dom/xrtest.rs
+++ b/components/script/dom/xrtest.rs
@@ -6,21 +6,30 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
-use crate::dom::bindings::codegen::Bindings::XRTestBinding;
-use crate::dom::bindings::reflector::{reflect_dom_object, Reflector};
+use crate::dom::bindings::codegen::Bindings::XRTestBinding::{
+    self, FakeXRDeviceInit, XRTestMethods,
+};
+use crate::dom::bindings::reflector::{reflect_dom_object, DomObject, Reflector};
 use crate::dom::bindings::root::DomRoot;
+use crate::dom::fakexrdevicecontroller::FakeXRDeviceController;
 use crate::dom::globalscope::GlobalScope;
+use crate::dom::promise::Promise;
 use dom_struct::dom_struct;
+use std::cell::Cell;
+use std::rc::Rc;
+use webvr_traits::WebVRMsg;
 
 #[dom_struct]
 pub struct XRTest {
     reflector: Reflector,
+    session_started: Cell<bool>,
 }
 
 impl XRTest {
     pub fn new_inherited() -> XRTest {
         XRTest {
             reflector: Reflector::new(),
+            session_started: Cell::new(false),
         }
     }
 
@@ -32,3 +41,24 @@ impl XRTest {
         )
     }
 }
+
+impl XRTestMethods for XRTest {
+    fn SimulateDeviceConnection(&self, init: &FakeXRDeviceInit) -> Rc<Promise> {
+        let p = Promise::new(&self.global());
+
+        if !init.supportsImmersive || self.session_started.get() {
+            p.reject_native(&());
+            return p;
+        }
+
+        self.session_started.set(true);
+        self.global()
+            .as_window()
+            .webvr_thread()
+            .unwrap()
+            .send(WebVRMsg::CreateMockDisplay);
+        p.resolve_native(&FakeXRDeviceController::new(&self.global()));
+
+        p
+    }
+}