diff --git a/crates/gpui3/src/app.rs b/crates/gpui3/src/app.rs
index dbe53603cd..ad8e861b69 100644
--- a/crates/gpui3/src/app.rs
+++ b/crates/gpui3/src/app.rs
@@ -1,6 +1,10 @@
+mod model_context;
+
+pub use model_context::*;
+
 use crate::{
-    current_platform, AnyWindowHandle, Context, LayoutId, MainThreadOnly, Platform, Reference,
-    RootView, TextSystem, Window, WindowContext, WindowHandle, WindowId,
+    current_platform, AnyWindowHandle, Context, LayoutId, MainThreadOnly, Platform, RootView,
+    TextSystem, Window, WindowContext, WindowHandle, WindowId,
 };
 use anyhow::{anyhow, Result};
 use collections::{HashMap, VecDeque};
@@ -274,94 +278,6 @@ impl AsyncContext {
     }
 }
 
-pub struct ModelContext<'a, T> {
-    app: Reference<'a, AppContext>,
-    entity_type: PhantomData<T>,
-    entity_id: EntityId,
-}
-
-impl<'a, T: Send + Sync + 'static> ModelContext<'a, T> {
-    pub(crate) fn mutable(app: &'a mut AppContext, entity_id: EntityId) -> Self {
-        Self {
-            app: Reference::Mutable(app),
-            entity_type: PhantomData,
-            entity_id,
-        }
-    }
-
-    // todo!
-    // fn update<R>(&mut self, update: impl FnOnce(&mut T, &mut Self) -> R) -> R {
-    //     let mut entity = self
-    //         .app
-    //         .entities
-    //         .get_mut(self.entity_id)
-    //         .unwrap()
-    //         .take()
-    //         .unwrap();
-    //     let result = update(entity.downcast_mut::<T>().unwrap(), self);
-    //     self.app
-    //         .entities
-    //         .get_mut(self.entity_id)
-    //         .unwrap()
-    //         .replace(entity);
-    //     result
-    // }
-
-    pub fn handle(&self) -> WeakHandle<T> {
-        WeakHandle {
-            id: self.entity_id,
-            entity_type: PhantomData,
-        }
-    }
-
-    pub fn observe<E: Send + Sync + 'static>(
-        &mut self,
-        handle: &Handle<E>,
-        on_notify: impl Fn(&mut T, Handle<E>, &mut ModelContext<'_, T>) + Send + Sync + 'static,
-    ) {
-        let this = self.handle();
-        let handle = handle.downgrade();
-        self.app
-            .observers
-            .entry(handle.id)
-            .or_default()
-            .push(Arc::new(move |cx| {
-                if let Some((this, handle)) = this.upgrade(cx).zip(handle.upgrade(cx)) {
-                    this.update(cx, |this, cx| on_notify(this, handle, cx));
-                    true
-                } else {
-                    false
-                }
-            }));
-    }
-
-    pub fn notify(&mut self) {
-        self.app
-            .pending_effects
-            .push_back(Effect::Notify(self.entity_id));
-    }
-}
-
-impl<'a, T: 'static> Context for ModelContext<'a, T> {
-    type EntityContext<'b, 'c, U: Send + Sync + 'static> = ModelContext<'b, U>;
-    type Result<U> = U;
-
-    fn entity<U: Send + Sync + 'static>(
-        &mut self,
-        build_entity: impl FnOnce(&mut Self::EntityContext<'_, '_, U>) -> U,
-    ) -> Handle<U> {
-        self.app.entity(build_entity)
-    }
-
-    fn update_entity<U: Send + Sync + 'static, R>(
-        &mut self,
-        handle: &Handle<U>,
-        update: impl FnOnce(&mut U, &mut Self::EntityContext<'_, '_, U>) -> R,
-    ) -> R {
-        self.app.update_entity(handle, update)
-    }
-}
-
 slotmap::new_key_type! { pub struct EntityId; }
 
 pub struct Handle<T> {
diff --git a/crates/gpui3/src/app/model_context.rs b/crates/gpui3/src/app/model_context.rs
new file mode 100644
index 0000000000..6ad5a06a56
--- /dev/null
+++ b/crates/gpui3/src/app/model_context.rs
@@ -0,0 +1,90 @@
+use crate::{AppContext, Context, Effect, EntityId, Handle, Reference, WeakHandle};
+use std::{marker::PhantomData, sync::Arc};
+
+pub struct ModelContext<'a, T> {
+    app: Reference<'a, AppContext>,
+    entity_type: PhantomData<T>,
+    entity_id: EntityId,
+}
+
+impl<'a, T: Send + Sync + 'static> ModelContext<'a, T> {
+    pub(crate) fn mutable(app: &'a mut AppContext, entity_id: EntityId) -> Self {
+        Self {
+            app: Reference::Mutable(app),
+            entity_type: PhantomData,
+            entity_id,
+        }
+    }
+
+    // todo!
+    // fn update<R>(&mut self, update: impl FnOnce(&mut T, &mut Self) -> R) -> R {
+    //     let mut entity = self
+    //         .app
+    //         .entities
+    //         .get_mut(self.entity_id)
+    //         .unwrap()
+    //         .take()
+    //         .unwrap();
+    //     let result = update(entity.downcast_mut::<T>().unwrap(), self);
+    //     self.app
+    //         .entities
+    //         .get_mut(self.entity_id)
+    //         .unwrap()
+    //         .replace(entity);
+    //     result
+    // }
+
+    pub fn handle(&self) -> WeakHandle<T> {
+        WeakHandle {
+            id: self.entity_id,
+            entity_type: PhantomData,
+        }
+    }
+
+    pub fn observe<E: Send + Sync + 'static>(
+        &mut self,
+        handle: &Handle<E>,
+        on_notify: impl Fn(&mut T, Handle<E>, &mut ModelContext<'_, T>) + Send + Sync + 'static,
+    ) {
+        let this = self.handle();
+        let handle = handle.downgrade();
+        self.app
+            .observers
+            .entry(handle.id)
+            .or_default()
+            .push(Arc::new(move |cx| {
+                if let Some((this, handle)) = this.upgrade(cx).zip(handle.upgrade(cx)) {
+                    this.update(cx, |this, cx| on_notify(this, handle, cx));
+                    true
+                } else {
+                    false
+                }
+            }));
+    }
+
+    pub fn notify(&mut self) {
+        self.app
+            .pending_effects
+            .push_back(Effect::Notify(self.entity_id));
+    }
+}
+
+impl<'a, T: 'static> Context for ModelContext<'a, T> {
+    type EntityContext<'b, 'c, U: Send + Sync + 'static> = ModelContext<'b, U>;
+    type Result<U> = U;
+
+    fn entity<U: Send + Sync + 'static>(
+        &mut self,
+        build_entity: impl FnOnce(&mut Self::EntityContext<'_, '_, U>) -> U,
+    ) -> Handle<U> {
+        self.app.entity(build_entity)
+    }
+
+    fn update_entity<U: Send + Sync + 'static, R>(
+        &mut self,
+        handle: &Handle<U>,
+        update: impl FnOnce(&mut U, &mut Self::EntityContext<'_, '_, U>) -> R,
+    ) -> R {
+        self.app.update_entity(handle, update)
+    }
+}
diff --git a/crates/gpui3/src/platform/test.rs b/crates/gpui3/src/platform/test.rs
index 8c418eb9c1..3b709f503f 100644
--- a/crates/gpui3/src/platform/test.rs
+++ b/crates/gpui3/src/platform/test.rs
@@ -9,53 +9,54 @@ impl TestPlatform {
     }
 }
 
+// todo!("implement out what our tests needed in GPUI 1")
 impl Platform for TestPlatform {
     fn dispatcher(&self) -> std::sync::Arc<dyn crate::PlatformDispatcher> {
-        todo!()
+        unimplemented!()
     }
 
     fn text_system(&self) -> std::sync::Arc<dyn crate::PlatformTextSystem> {
-        todo!()
+        unimplemented!()
     }
 
     fn run(&self, _on_finish_launching: Box<dyn FnOnce()>) {
-        todo!()
+        unimplemented!()
     }
 
     fn quit(&self) {
-        todo!()
+        unimplemented!()
     }
 
     fn restart(&self) {
-        todo!()
+        unimplemented!()
     }
 
     fn activate(&self, _ignoring_other_apps: bool) {
-        todo!()
+        unimplemented!()
     }
 
     fn hide(&self) {
-        todo!()
+        unimplemented!()
     }
 
     fn hide_other_apps(&self) {
-        todo!()
+        unimplemented!()
     }
 
     fn unhide_other_apps(&self) {
-        todo!()
+        unimplemented!()
     }
 
     fn screens(&self) -> Vec<std::rc::Rc<dyn crate::PlatformScreen>> {
-        todo!()
+        unimplemented!()
     }
 
     fn screen_by_id(&self, _id: ScreenId) -> Option<std::rc::Rc<dyn crate::PlatformScreen>> {
-        todo!()
+        unimplemented!()
     }
 
     fn main_window(&self) -> Option<crate::AnyWindowHandle> {
-        todo!()
+        unimplemented!()
     }
 
     fn open_window(
@@ -63,93 +64,93 @@ impl Platform for TestPlatform {
         _handle: crate::AnyWindowHandle,
         _options: crate::WindowOptions,
     ) -> Box<dyn crate::PlatformWindow> {
-        todo!()
+        unimplemented!()
     }
 
     fn open_url(&self, _url: &str) {
-        todo!()
+        unimplemented!()
     }
 
     fn on_open_urls(&self, _callback: Box<dyn FnMut(Vec<String>)>) {
-        todo!()
+        unimplemented!()
     }
 
     fn prompt_for_paths(
         &self,
         _options: crate::PathPromptOptions,
     ) -> futures::channel::oneshot::Receiver<Option<Vec<std::path::PathBuf>>> {
-        todo!()
+        unimplemented!()
     }
 
     fn prompt_for_new_path(
         &self,
         _directory: &std::path::Path,
     ) -> futures::channel::oneshot::Receiver<Option<std::path::PathBuf>> {
-        todo!()
+        unimplemented!()
     }
 
     fn reveal_path(&self, _path: &std::path::Path) {
-        todo!()
+        unimplemented!()
     }
 
     fn on_become_active(&self, _callback: Box<dyn FnMut()>) {
-        todo!()
+        unimplemented!()
     }
 
     fn on_resign_active(&self, _callback: Box<dyn FnMut()>) {
-        todo!()
+        unimplemented!()
     }
 
     fn on_quit(&self, _callback: Box<dyn FnMut()>) {
-        todo!()
+        unimplemented!()
     }
 
     fn on_reopen(&self, _callback: Box<dyn FnMut()>) {
-        todo!()
+        unimplemented!()
     }
 
     fn on_event(&self, _callback: Box<dyn FnMut(crate::Event) -> bool>) {
-        todo!()
+        unimplemented!()
     }
 
     fn os_name(&self) -> &'static str {
-        todo!()
+        unimplemented!()
     }
 
     fn os_version(&self) -> anyhow::Result<crate::SemanticVersion> {
-        todo!()
+        unimplemented!()
     }
 
     fn app_version(&self) -> anyhow::Result<crate::SemanticVersion> {
-        todo!()
+        unimplemented!()
     }
 
     fn app_path(&self) -> anyhow::Result<std::path::PathBuf> {
-        todo!()
+        unimplemented!()
     }
 
     fn local_timezone(&self) -> time::UtcOffset {
-        todo!()
+        unimplemented!()
     }
 
     fn path_for_auxiliary_executable(&self, _name: &str) -> anyhow::Result<std::path::PathBuf> {
-        todo!()
+        unimplemented!()
     }
 
     fn set_cursor_style(&self, _style: crate::CursorStyle) {
-        todo!()
+        unimplemented!()
     }
 
     fn should_auto_hide_scrollbars(&self) -> bool {
-        todo!()
+        unimplemented!()
     }
 
     fn write_to_clipboard(&self, _item: crate::ClipboardItem) {
-        todo!()
+        unimplemented!()
     }
 
     fn read_from_clipboard(&self) -> Option<crate::ClipboardItem> {
-        todo!()
+        unimplemented!()
     }
 
     fn write_credentials(
@@ -158,14 +159,14 @@ impl Platform for TestPlatform {
         _username: &str,
         _password: &[u8],
     ) -> anyhow::Result<()> {
-        todo!()
+        unimplemented!()
     }
 
     fn read_credentials(&self, _url: &str) -> anyhow::Result<Option<(String, Vec<u8>)>> {
-        todo!()
+        unimplemented!()
     }
 
     fn delete_credentials(&self, _url: &str) -> anyhow::Result<()> {
-        todo!()
+        unimplemented!()
     }
 }