n8n/packages/cli/test/extend-expect.ts

expect.extend({
	toBeEmptyArray(this: jest.MatcherContext, actual: unknown) {
		const pass = Array.isArray(actual) && actual.length === 0;

		return {
			pass,
			message: pass
				? () => `Expected ${actual} to be an empty array`
				: () => `Expected ${actual} not to be an empty array`,
		};
	},

	toBeEmptySet(this: jest.MatcherContext, actual: unknown) {
		const pass = actual instanceof Set && actual.size === 0;

		return {
			pass,
			message: pass
				? () => `Expected ${[...actual]} to be an empty set`
				: () => `Expected ${actual} not to be an empty set`,
		};
	},

	toBeSetContaining(this: jest.MatcherContext, actual: unknown, ...expectedElements: string[]) {
		const pass = actual instanceof Set && expectedElements.every((e) => actual.has(e));

		return {
			pass,
			message: pass
				? () => `Expected ${[...actual]} to be a set containing ${expectedElements}`
				: () => `Expected ${actual} not to be a set containing ${expectedElements}`,
		};
	},
});