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Create mocks with the mock function from bun:test.
/icons/typescript.svgtest.ts
import {test, expect, mock} from 'bun:test';

const random = mock(() => Math.random());
The mock function can accept arguments.
/icons/typescript.svgtest.ts
import {test, expect, mock} from 'bun:test';

const random = mock((multiplier: number) => multiplier * Math.random());
The result of mock() is a new function that’s been decorated with some additional properties.
/icons/typescript.svgtest.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 }
//  ]
These extra properties make it possible to write expect assertions about usage of the mock function, including how many times it was called, the arguments, and the return values.
/icons/typescript.svgtest.ts
import {test, expect, mock} from 'bun:test';

const random = mock((multiplier: number) => multiplier * Math.random());

test('random', async () => {
	const a = random(1);
	const b = random(2);
	const c = random(3);

	expect(random).toHaveBeenCalled();
	expect(random).toHaveBeenCalledTimes(3);
	expect(random.mock.args).toEqual([[1], [2], [3]]);
	expect(random.mock.results[0]).toEqual({type: 'return', value: a});
});
See Docs > Test Runner > Mocks for complete documentation on mocking with the Bun test runner.
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