diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 7788624..bcf4f82 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -60,3 +60,12 @@ jobs:
       - run: "mise clippy"
       - run: "mise bevy_lint"
       - run: "mise test"
+
+      - uses: taiki-e/install-action@cargo-llvm-cov
+      - name: Collect coverage data
+        run: cargo llvm-cov nextest
+      - name: Upload coverage reports to Codecov
+        uses: codecov/codecov-action@v5
+        with:
+          token: ${{ secrets.CODECOV_TOKEN }}
+          slug: ada-x64/qproj
diff --git a/.zed/settings.json b/.zed/settings.json
index 210d235..f101d92 100644
--- a/.zed/settings.json
+++ b/.zed/settings.json
@@ -3,18 +3,19 @@
     "rust-analyzer": {
       "initialization_options": {
         "cargo": {
-          "features": "all"
+          "features": "all",
         },
         "check": {
           "command": "clippy",
-          "extraArgs": ["--locked", "--target-dir=target/rust-analyzer"]
-        }
-      }
-    }
+          "extraArgs": ["--locked", "--target-dir=target/rust-analyzer"],
+          "workspace": false,
+        },
+      },
+    },
   },
   "languages": {
     "Python": {
-      "language_servers": ["ruff", "basedpyright"]
-    }
-  }
+      "language_servers": ["ruff", "basedpyright"],
+    },
+  },
 }
diff --git a/Cargo.lock b/Cargo.lock
index ea9b266..13da645 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -5587,6 +5587,7 @@ dependencies = [
  "bevy",
  "bevy-inspector-egui",
  "bevy_asset_loader",
+ "bevy_test_harness",
  "bitflags 2.10.0",
  "itertools 0.14.0",
  "serde",
@@ -7045,18 +7046,18 @@ checksum = "6df3dc4292935e51816d896edcd52aa30bc297907c26167fec31e2b0c6a32524"
 
 [[package]]
 name = "zerocopy"
-version = "0.8.34"
+version = "0.8.35"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "71ddd76bcebeed25db614f82bf31a9f4222d3fbba300e6fb6c00afa26cbd4d9d"
+checksum = "fdea86ddd5568519879b8187e1cf04e24fce28f7fe046ceecbce472ff19a2572"
 dependencies = [
  "zerocopy-derive",
 ]
 
 [[package]]
 name = "zerocopy-derive"
-version = "0.8.34"
+version = "0.8.35"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d8187381b52e32220d50b255276aa16a084ec0a9017a0ca2152a1f55c539758d"
+checksum = "0c15e1b46eff7c6c91195752e0eeed8ef040e391cdece7c25376957d5f15df22"
 dependencies = [
  "proc-macro2",
  "quote",
diff --git a/crates/tfw/Cargo.toml b/crates/tfw/Cargo.toml
index aaa8e59..33d8e3e 100644
--- a/crates/tfw/Cargo.toml
+++ b/crates/tfw/Cargo.toml
@@ -18,6 +18,9 @@ anyhow = "1.0.99"
 strum = { version = "0.27.2", features = ["derive"] }
 variadics_please = "1.1.0"
 
+# local
+bevy_test_harness = {path="../test_harness"}
+
 [dev-dependencies]
 # just for a few inspector things... should really fork them
 bevy-inspector-egui = "0.36"
diff --git a/crates/tfw/tests/app/mod.rs b/crates/tfw/tests/app/mod.rs
index 0d5087b..7f3d2b0 100644
--- a/crates/tfw/tests/app/mod.rs
+++ b/crates/tfw/tests/app/mod.rs
@@ -1,12 +1,10 @@
 pub mod screen;
 pub mod service;
-pub mod util;
 
 pub mod prelude {
     pub use super::AppPlugin;
     pub use super::screen::prelude::*;
     pub use super::service::prelude::*;
-    pub use super::util::prelude::*;
     pub use bevy::prelude::*;
     pub use tfw::prelude::*;
 }
diff --git a/crates/tfw/tests/app/util/app_ext.rs b/crates/tfw/tests/app/util/app_ext.rs
deleted file mode 100644
index d235ea6..0000000
--- a/crates/tfw/tests/app/util/app_ext.rs
+++ /dev/null
@@ -1,15 +0,0 @@
-use crate::prelude::*;
-
-pub trait AppExt {
-    fn add_step<M>(&mut self, step: u32, system: impl IntoSystem<(), (), M>) -> &mut Self;
-}
-impl AppExt for App {
-    /// Registers a system which runs in PostUpdate (after all screen events have occured).
-    /// Will only run if the state is set to the specified value.
-    fn add_step<M>(&mut self, step: u32, system: impl IntoSystem<(), (), M>) -> &mut Self {
-        self.add_systems(
-            PostUpdate,
-            system.run_if(in_state(Step(step))).after(log_step),
-        )
-    }
-}
diff --git a/crates/tfw/tests/app/util/commands_ext.rs b/crates/tfw/tests/app/util/commands_ext.rs
deleted file mode 100644
index 5f2b53b..0000000
--- a/crates/tfw/tests/app/util/commands_ext.rs
+++ /dev/null
@@ -1,123 +0,0 @@
-use bevy::ecs::query::QueryFilter;
-use bevy_inspector_egui::bevy_inspector::{
-    guess_entity_name,
-    hierarchy::{Hierarchy, SelectedEntities},
-};
-
-use crate::prelude::*;
-
-pub trait CommandsExt {
-    fn log_hierarchy(&mut self);
-    fn find_entity(&mut self, name: impl ToString);
-    fn find_no_entity(&mut self, name: impl ToString);
-    fn find_entity_filtered<F: QueryFilter + 'static>(&mut self, name: impl ToString);
-    fn find_no_entity_filtered<F: QueryFilter + 'static>(&mut self, name: impl ToString);
-    fn find_entity_with<C: Component + PartialEq>(
-        &mut self,
-        name: impl ToString,
-        value: C,
-        invert: bool,
-    );
-}
-impl<'w, 's> CommandsExt for Commands<'w, 's> {
-    fn log_hierarchy(&mut self) {
-        self.run_system_cached(|world: &mut World| {
-            let h = Hierarchy {
-                world,
-                selected: &mut SelectedEntities::default(),
-                context_menu: None,
-                shortcircuit_entity: None,
-                extra_state: &mut (),
-            };
-
-            let mut root_query = h.world.query_filtered::<Entity, Without<ChildOf>>();
-            let entities: Vec<_> = root_query.iter(h.world).collect();
-            let mut output = String::new();
-            log_hierarchy_inner(world, &mut output, entities, 0);
-            info!("{output}")
-        });
-    }
-    fn find_entity(&mut self, name: impl ToString) {
-        self.run_system_cached_with(find_entity, (name.to_string(), false));
-    }
-    fn find_no_entity(&mut self, name: impl ToString) {
-        self.run_system_cached_with(find_entity, (name.to_string(), true));
-    }
-    fn find_entity_filtered<F: QueryFilter + 'static>(&mut self, name: impl ToString) {
-        self.run_system_cached_with(find_entity_filtered::<F>, (name.to_string(), false));
-    }
-    fn find_no_entity_filtered<F: QueryFilter + 'static>(&mut self, name: impl ToString) {
-        self.run_system_cached_with(find_entity_filtered::<F>, (name.to_string(), true));
-    }
-    fn find_entity_with<C: Component + PartialEq>(
-        &mut self,
-        name: impl ToString,
-        value: C,
-        invert: bool,
-    ) {
-        self.run_system_cached_with(find_entity_with, (name.to_string(), invert, value));
-    }
-}
-
-fn log_hierarchy_inner(world: &mut World, output: &mut String, entities: Vec<Entity>, depth: u32) {
-    for &entity in &entities {
-        let entity_name = guess_entity_name(world, entity);
-        let mut tags = vec![];
-        if world.entity(entity).get::<Persistent>().is_some() {
-            tags.push("Persistent");
-        }
-        if world.entity(entity).get::<Observer>().is_some() {
-            tags.push("Observer");
-        }
-        let indent = (0..depth).map(|_| "-").collect::<Vec<_>>().join("");
-        #[allow(clippy::obfuscated_if_else)]
-        let tags = (!tags.is_empty())
-            .then(|| format!("<{}>", tags.join(", ")))
-            .unwrap_or_default();
-
-        *output = format!("{output}\n{indent}> {entity_name} {tags}");
-
-        if let Some(children) = world.entity(entity).get::<Children>() {
-            let children = children.iter().collect::<Vec<Entity>>();
-            log_hierarchy_inner(world, output, children, depth + 1);
-        }
-    }
-}
-
-/// Searches for an entity with the given [Name] component.
-/// This _will not_ show entities marked with [Internal], including Observers.
-fn find_entity(input: In<(String, bool)>, q: Query<&Name>, mut commands: Commands) {
-    let (name, invert) = input.0;
-    let any = q.iter().any(|ename| (**ename).eq(&name));
-    if (invert && any) || (!invert && !any) {
-        commands.write_message(AppExit::error());
-    }
-}
-
-/// Searches for an entity with the given [Name] component
-fn find_entity_filtered<F: QueryFilter>(
-    input: In<(String, bool)>,
-    q: Query<&Name, F>,
-    mut commands: Commands,
-) {
-    let (name, invert) = input.0;
-    let any = q.iter().any(|ename| (**ename).eq(&name));
-    if (invert && any) || (!invert && !any) {
-        commands.write_message(AppExit::error());
-    }
-}
-
-/// Searches for an entity with the given [Name] and component C.
-fn find_entity_with<C: Component + PartialEq>(
-    input: In<(String, bool, C)>,
-    q: Query<(&Name, &C)>,
-    mut commands: Commands,
-) {
-    let (name, invert, value) = input.0;
-    let any = q
-        .iter()
-        .any(|(ename, c)| (**ename).eq(&name) && *c == value);
-    if (invert && any) || (!invert && !any) {
-        commands.write_message(AppExit::error());
-    }
-}
diff --git a/crates/tfw/tests/app/util/data.rs b/crates/tfw/tests/app/util/data.rs
deleted file mode 100644
index 121ded9..0000000
--- a/crates/tfw/tests/app/util/data.rs
+++ /dev/null
@@ -1,4 +0,0 @@
-use crate::prelude::*;
-
-#[derive(States, Debug, Default, Deref, DerefMut, Clone, Copy, Hash, Eq, PartialEq)]
-pub struct Step(pub u32);
diff --git a/crates/tfw/tests/app/util/mod.rs b/crates/tfw/tests/app/util/mod.rs
deleted file mode 100644
index 1c4c3a2..0000000
--- a/crates/tfw/tests/app/util/mod.rs
+++ /dev/null
@@ -1,11 +0,0 @@
-mod app_ext;
-mod commands_ext;
-mod data;
-mod runner;
-
-pub mod prelude {
-    pub use super::app_ext::*;
-    pub use super::commands_ext::*;
-    pub use super::data::*;
-    pub use super::runner::*;
-}
diff --git a/crates/tfw/tests/app/util/runner.rs b/crates/tfw/tests/app/util/runner.rs
deleted file mode 100644
index ebfb1cc..0000000
--- a/crates/tfw/tests/app/util/runner.rs
+++ /dev/null
@@ -1,131 +0,0 @@
-use bevy::{
-    app::ScheduleRunnerPlugin,
-    core_pipeline::CorePipelinePlugin,
-    diagnostic::FrameCountPlugin,
-    log::LogPlugin,
-    mesh::MeshPlugin,
-    pbr::PbrPlugin,
-    prelude::*,
-    render::{
-        RenderPlugin,
-        settings::{RenderCreation, WgpuSettings},
-    },
-    scene::ScenePlugin,
-    state::app::StatesPlugin,
-    time::TimePlugin,
-    window::ExitCondition,
-};
-
-use crate::prelude::*;
-
-pub trait TestFn: Fn(&mut App) {}
-impl<T> TestFn for T where T: Fn(&mut App) {}
-
-#[derive(Debug)]
-pub struct TestRunnerPlugin {
-    pub timeout: f32,
-}
-impl Default for TestRunnerPlugin {
-    fn default() -> Self {
-        Self { timeout: 5. } // 5 sec
-    }
-}
-impl Plugin for TestRunnerPlugin {
-    fn build(&self, app: &mut App) {
-        app.add_plugins((
-            TaskPoolPlugin::default(),
-            FrameCountPlugin,
-            TimePlugin,
-            ScheduleRunnerPlugin::default(),
-            LogPlugin::default(),
-            WindowPlugin {
-                primary_window: Some(Window {
-                    title: "Headless test".into(),
-                    resizable: true,
-                    focused: true,
-                    visible: false,
-                    desired_maximum_frame_latency: None,
-                    ..Default::default()
-                }),
-                primary_cursor_options: None,
-                close_when_requested: true,
-                exit_condition: ExitCondition::OnPrimaryClosed,
-            },
-            AssetPlugin::default(),
-            RenderPlugin {
-                render_creation: RenderCreation::Automatic(WgpuSettings {
-                    backends: None,
-                    ..Default::default()
-                }),
-                ..Default::default()
-            },
-            ImagePlugin::default(),
-            CorePipelinePlugin,
-            MeshPlugin,
-            PbrPlugin {
-                prepass_enabled: false,
-                add_default_deferred_lighting_plugin: false,
-                use_gpu_instance_buffer_builder: false,
-                ..Default::default()
-            },
-            StatesPlugin,
-            ScenePlugin,
-        ));
-
-        let timeout = self.timeout;
-        app.add_systems(
-            Update,
-            move |time: Res<Time<Real>>, mut events: MessageWriter<AppExit>| {
-                let elapsed = time.elapsed_secs();
-                if elapsed > timeout {
-                    error!("Timeout after {elapsed}s");
-                    events.write(AppExit::error());
-                }
-            },
-        );
-        app.add_systems(PostUpdate, (log_step, check_exit).chain());
-
-        app.init_state::<Step>();
-    }
-}
-
-pub fn log_step(step: Res<State<Step>>, mut local_step: Local<u32>) {
-    info_once!("Step = {}", ***step); // when step = 0
-    if ***step != *local_step {
-        *local_step = ***step;
-        info!("Step = {}", ***step);
-    }
-}
-
-fn check_exit(mut reader: MessageReader<AppExit>) {
-    for msg in reader.read() {
-        error!("Obtained exit message {msg:?}");
-    }
-}
-
-#[test]
-fn timeout() {
-    let mut app = App::new();
-    app.add_plugins(TestRunnerPlugin { timeout: 0.5 });
-    assert!(app.run().is_error());
-}
-
-#[test]
-fn explicit_failure() {
-    let mut app = App::new();
-    app.add_plugins(TestRunnerPlugin::default());
-    app.add_systems(First, |mut commands: Commands| {
-        commands.write_message(AppExit::error());
-    });
-    assert!(app.run().is_error());
-}
-
-#[test]
-fn explicit_success() {
-    let mut app = App::new();
-    app.add_plugins(TestRunnerPlugin::default());
-    app.add_systems(First, |mut commands: Commands| {
-        commands.write_message(AppExit::Success);
-    });
-    assert!(app.run().is_success());
-}
diff --git a/crates/tfw/tests/screen/entity_scoping.rs b/crates/tfw/tests/screen/entity_scoping.rs
index 124e344..6d1a588 100644
--- a/crates/tfw/tests/screen/entity_scoping.rs
+++ b/crates/tfw/tests/screen/entity_scoping.rs
@@ -1,3 +1,4 @@
+use bevy_test_harness::prelude::*;
 use tfw::{TfwPlugin, TfwSettings};
 
 use crate::prelude::*;
diff --git a/crates/tfw/tests/screen/mod.rs b/crates/tfw/tests/screen/mod.rs
index 819b6b8..5c411a2 100644
--- a/crates/tfw/tests/screen/mod.rs
+++ b/crates/tfw/tests/screen/mod.rs
@@ -2,6 +2,7 @@ mod entity_scoping;
 mod system_scoping;
 
 use crate::prelude::*;
+use bevy_test_harness::TestRunnerPlugin;
 use tfw::{TfwPlugin, TfwSettings};
 
 // the rest of the tests use non-blocking asset loading to circumvent the delay.
diff --git a/crates/tfw/tests/screen/system_scoping.rs b/crates/tfw/tests/screen/system_scoping.rs
index e07be66..e0443fc 100644
--- a/crates/tfw/tests/screen/system_scoping.rs
+++ b/crates/tfw/tests/screen/system_scoping.rs
@@ -1,3 +1,4 @@
+use bevy_test_harness::prelude::*;
 use tfw::{TfwPlugin, TfwSettings};
 
 use crate::prelude::*;