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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);
});
```
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