import "mocha";
import { expect } from "chai";
import { is } from "../helpers";

describe('Thunk factory "is.natural"', () => {
	it("recognizes natural numbers", () => {
		const thunk = is.natural();
		const naturals = Array.from({ length: 10 }, (_, i) => i); // 0, 1, ...
		const invalid = naturals.map(n => ~n); // -1, -2, ...

		for (const value of naturals)
			expect(thunk(value)).to.be.true;

		for (const value of invalid)
			expect(thunk(value)).to.be.false;
	});

	it("accepts optional flag, indicating naturalness of the zero", () => {
		expect(is.natural()(0)).to.be.true;
		expect(is.natural(true)(0)).to.be.true;
		expect(is.natural(false)(0)).to.be.false;
	});
});