Error when testing with practical:mocha

Hey guys I’m trying to test some of my methods, but I keep getting the following error:

Error: Match error: Expected string, got undefined
    at exports.check (packages/check/match.js:34:1)
    at Object.deleteComment (server/comments/methods.js:43:3) <= Offending line
    at Test.<anonymous> (test/comments.tests.js:38:19)
    at run (packages/practicalmeteor:mocha-core/server.js:34:29)
    at Context.wrappedFunction (packages/practicalmeteor:mocha-core/server.js:63:33)

And the offending line on the code: comment/methods.js

Meteor.methods({

	...omitted code

	deleteComment: (authorId, commentId) => {
		check(commentId, String); // <= [ERROR]: offending line
		check(authorId, String);

		const comment = Comments.findOne(commentId);

		if (comment.owner !== this.authorId) {
			throw new Meteor.Error('not-authorized', alert('You can only delete your own comments'));
		}
		Comments.remove(commentId);
	}
})

tests: comments.test.js

/* eslint-env mocha */

import { Meteor } from 'meteor/meteor'
import { Random } from 'meteor/random'
import { expect } from 'meteor/practicalmeteor:chai'
import { assert } from 'meteor/practicalmeteor:chai'

import '../server/comments/methods.js'
import '../collections/comments.js'



if (Meteor.isServer) {
	describe('Comments', () => {
		describe('methods', () => {

			const userId = Random.id();
			const fritkotId = Random.id();
			const testDate = new Date();
		

			let commentId;

			beforeEach(() => {
				Comments.remove(({}));
				commentId = Comments.insert({
					body: 'Test-content',
					author: userId,
					fritkotId: fritkotId,
					createdAt: testDate
				});
			});

			it('can delete owned comments', () => {
				const deleteComment = Meteor.server.method_handlers['deleteComment'];
				const invocation = { userId };

				deleteComment.apply(invocation, [commentId]);
				// assert.equal(Comments.find().count(), 0);
				expect( () => { Comments.find().count()} ).to.equal(0)
			})
		})
	}) /* End of Comments */
}

You’ve probably figured this out by now but you check (or verify) that commentId is a String on that line. When you call your method commendId is undefined, not a String