Expect.extend method | bun:test module | Bun

Register new custom matchers.

An object containing the matchers to register, where each key is the matcher name, and its value the implementation function. The function must satisfy: (actualValue, ...matcherInstantiationArguments) => { pass: true|false, message: () => string }

expect.extend({
toBeWithinRange(actual, min, max) {
if (typeof actual !== 'number' || typeof min !== 'number' || typeof max !== 'number')
throw new Error('Invalid usage');
const pass = actual >= min && actual max;
return {
pass: pass,
message: () => `expected ${this.utils.printReceived(actual)} ` +
(pass ? `not to be`: `to be`) + ` within range ${this.utils.printExpected(`${min} .. ${max}`)}`,
};
},
});

test('some test', () => {
expect(50).toBeWithinRange(0, 100); // will pass
expect(50).toBeWithinRange(100, 200); // will fail
expect(50).toBe(expect.toBeWithinRange(0, 100)); // will pass
expect(50).toBe(expect.not.toBeWithinRange(100, 200)); // will pass
});

If the types has been defined through declaration merging, enforce it. Otherwise enforce the generic custom matcher signature.