feat: Support Deno.beforeEach to run a function before each of the tests

[getspooky]

Description

Runs a function before each of the tests in this file runs. If the function returns a promise, Deno waits for that promise to resolve before running the test.

Deno.beforeEach(function(): void {
  // 
});

Deno.test("Hello Test", () => {
  assert("Hello");
});

Motivation

Most times you have setup work that has to happen before the tests run. For example consider when you have several tests interact with a database of cities. You have a method initializeCityDatabase() that has to be called before each of these tests
Deno provides helper functions Deno.beforeEach to handle this.

beforeEach(() => {
  initializeCityDatabase();
});

Deno.test("city database has Casablanca", () => {
  assert(isCity("Casablanca"));
});

[caspervonb]

Let me preface this with saying that I appreciate the effort, but...

I am very strongly against sticking this in the test runner.
It is preferable to use composition instead.

Deno.test("myTestWithdatabase", withDatabase(async function(db) {
  // ...
});

Global hooks encourages global state, which is a mistake.
I don't intend us to hop on the bad design bandwagon just because other testing frameworks in JavaScript has done it in the past.

You're better off using helper functions that to do the specific setup and teardown that you need for you and provide you with a closure that has the required state as this can be factored into a test_helper module be re-used, composed, etc.

If you really want to use global state hooks you can do something like this:

import { beforeEach, afterEach, withHooks } from "./test_util.ts";

beforeEach(async function() {
});

afterEach(async function() {
});

Deno.test("", withHooks(async function() {
});

[ry]

Thanks @getspooky - but I'm in agreement with Casper.

Maybe we need some better documentation or even a helper module in std/testing/ to communicate this pattern more effectively.

Closing without merge.

[ry]

I've opened an issue in std for adding a utility library for this functionality
denoland/std#931