We have event observer with a test

deps.ts

@@ -1 +1,7 @@
-export { assertEquals, assertThrowsAsync } from "testing/asserts.ts";
+/**
+ * assert()         - Expects a boolean value, throws if the value is false.
+ * assertEquals()   - Uses the equal comparison and throws if the actual and expected are not equal.
+ * assertStrictEq() - Compares actual and expected strictly, therefore for non-primitives the values must reference the same
+ */
+
+export { assert, assertEquals, assertStrictEq } from "testing/asserts.ts";

src/EventObserver.ts

@@ -0,0 +1,18 @@
+// https://www.sitepoint.com/javascript-design-patterns-observer-pattern/
+export class EventObserver {
+  constructor(public observers = [] as any) {}
+
+  subscribe(fn: any) {
+    this.observers.push(fn);
+  }
+
+  unsubscribe(fn: any) {
+    this.observers = this.observers.filter(
+      (subscriber: any) => subscriber !== fn
+    );
+  }
+
+  broadcast(data: any) {
+    this.observers.forEach((subscriber: any) => subscriber(data));
+  }
+}

src/new-test-pattern.ts

@@ -1,3 +1,4 @@
+import { EventObserver } from "../src/EventObserver";
 import { Vector2, vectors } from "./utilities/vectors";
 
 interface Delegate {
@@ -93,7 +94,9 @@ class DirectTowardsable implements Delegate {
     );
   }
 }
-
+/**
+ * this is not a delegate... it is shared state that can be pushed inside a delegate
+ */
 class Positionable {
   constructor(
     public position: Vector2,

test/new-test-patterns_test.ts

@@ -0,0 +1,40 @@
+import { assertEquals, assert } from "../deps.ts";
+import { EventObserver } from "../src/EventObserver.ts";
+/**
+ * SUBSCRIBE UNSUBSCRIBE
+ */
+Deno.test({
+  name: "SUBSCRIBE UNSUBSCRIBE",
+  fn(): void {
+    // Arrange
+    const observer = new EventObserver();
+    const fn = () => {};
+    observer.subscribe(fn);
+
+    // Act
+    observer.unsubscribe(fn);
+
+    // Assert
+    assertEquals(observer.observers.length, 0);
+  }
+});
+
+/**
+ * BROADCAST
+ */
+Deno.test({
+  name: "BROADCAST",
+  fn(): void {
+    // Arrange
+    const observer = new EventObserver();
+    let subscriberHasBeenCalled = false;
+    const fn = data => (subscriberHasBeenCalled = data);
+    observer.subscribe(fn);
+
+    // Act
+    observer.broadcast(true);
+
+    // Assert
+    assert(subscriberHasBeenCalled);
+  }
+});

tsconfig.json

@@ -9,6 +9,6 @@
     "forceConsistentCasingInFileNames": true,
     "resolveJsonModule": true
   },
-  "include": ["src/**/*"],
+  "include": ["src/**/*", "test/**/*"],
   "exclude": ["node_modules"]
 }