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+Create mocks with the `mock` function.
+
+```ts
+import { test, expect, mock } from "bun:test";
+const random = mock(() => Math.random());
+
+test("random", async () => {
+  const val = random();
+  expect(val).toBeGreaterThan(0);
+  expect(random).toHaveBeenCalled();
+  expect(random).toHaveBeenCalledTimes(1);
+});
+```
+
+The result of `mock()` is a new function that's been decorated with some additional properties.
+
+```ts
+import { mock } from "bun:test";
+const random = mock((multiplier: number) => multiplier * Math.random());
+
+random(2);
+random(10);
+
+random.mock.calls;
+// [[ 2 ], [ 10 ]]
+
+random.mock.results;
+//  [
+//    { type: "return", value: 0.6533907460954099 },
+//    { type: "return", value: 0.6452713933037312 }
+//  ]
+```
+
+## `.spyOn()`
+
+It's possible to track calls to a function without replacing it with a mock. Use `spyOn()` to create a spy; these spies can be passed to `.toHaveBeenCalled()` and `.toHaveBeenCalledTimes()`.
+
+```ts
+import { test, expect, spyOn } from "bun:test";
+
+const ringo = {
+  name: "Ringo",
+  sayHi() {
+    console.log(`Hello I'm ${this.name}`);
+  },
+};
+
+const spy = spyOn(ringo, "sayHi");
+
+test("spyon", () => {
+  expect(spy).toHaveBeenCalledTimes(0);
+  ringo.sayHi();
+  expect(spy).toHaveBeenCalledTimes(1);
+});
+```