From b7c6edb42612a55b34df92f24214020f388f36d3 Mon Sep 17 00:00:00 2001
From: Andre Popovitch <andre@popovit.ch>
Date: Fri, 9 Sep 2022 21:05:05 -0500
Subject: [PATCH] Add example of how to use TestPlugin

---
 Cargo.toml               | 10 +++++++++
 examples/README.md       |  1 +
 tests/automated_tests.rs | 48 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 59 insertions(+)
 create mode 100644 tests/automated_tests.rs

diff --git a/Cargo.toml b/Cargo.toml
index 226d640bcdff7d..08df30cafd446d 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -921,6 +921,16 @@ description = "Illustrates ticking `Timer` resources inside systems and handling
 category = "ECS (Entity Component System)"
 wasm = false
 
+[[example]]
+name = "automated_tests"
+path = "tests/automated_tests.rs"
+
+[package.metadata.example.automated_tests]
+name = "Automated Tests"
+description = "Illustrates how to test systems"
+category = "ECS (Entity Component System)"
+wasm = false
+
 # Games
 [[example]]
 name = "alien_cake_addict"
diff --git a/examples/README.md b/examples/README.md
index 8f8b57759727a7..e5d2c8b7b340d6 100644
--- a/examples/README.md
+++ b/examples/README.md
@@ -187,6 +187,7 @@ Example | Description
 
 Example | Description
 --- | ---
+[Automated Tests](../examples/ecs/automated_tests.rs) | Illustrates how to test systems
 [Component Change Detection](../examples/ecs/component_change_detection.rs) | Change detection on components
 [Custom Query Parameters](../examples/ecs/custom_query_param.rs) | Groups commonly used compound queries and query filters into a single type
 [ECS Guide](../examples/ecs/ecs_guide.rs) | Full guide to Bevy's ECS
diff --git a/tests/automated_tests.rs b/tests/automated_tests.rs
new file mode 100644
index 00000000000000..4675251677b27b
--- /dev/null
+++ b/tests/automated_tests.rs
@@ -0,0 +1,48 @@
+//! This example illustrates test systems.
+fn main() {
+    println!("This example is special! Run it with `cargo test --example automated_tests`.");
+    println!(
+        "Or use `cargo test --example automated_tests -- --nocapture` to see the debug output."
+    );
+}
+
+#[cfg(test)]
+mod test {
+    use bevy::prelude::*;
+
+    #[test]
+    fn simple_test() {
+        // Setup the app with the TestPlugins – these will run fine in tests and in CI.
+        // Note that many 3rd-party plugins will require DefaultPlugins, not just TestPlugins.
+        let mut app = App::new();
+        app.add_plugins(TestPlugins).add_system(increment);
+
+        // Spawn a new entity with a Counter component, and record its ID.
+        let counter_id = app.world.spawn().insert(Counter::default()).id();
+
+        // Simulate for a 10 frames
+        let num_frames = 10;
+        for _ in 0..num_frames {
+            app.update();
+        }
+
+        // Check that the counter was incremented 10 times.
+        let count = app.world.get::<Counter>(counter_id).unwrap().counter;
+        assert_eq!(count, num_frames);
+
+        println!("Success!");
+    }
+    // Define a system and a component that we can use in our test.
+    #[derive(Debug, Default, Component, Clone, Copy)]
+    struct Counter {
+        counter: u64,
+    }
+
+    /// Increment the counter every frame
+    fn increment(mut query: Query<&mut Counter>) {
+        for mut counter in query.iter_mut() {
+            counter.counter += 1;
+            println!("Counter: {}", counter.counter);
+        }
+    }
+}