feat: support async/await in jest tests (#105)

[thektan]

I created a babel.test.json to separate the babel configurations between the test and build scripts. I didn't use the const isTest = api.env('test'); in babel.config.js example from the jest docs so we could continue to use the babelMerge function in deepMerge.js as is.

But I'm also not sure what the implications would be if we only applied the following to the current babel.json instead of creating a separate babel.test.json.

{
	"presets": [
		[
			"@babel/preset-env",
			{
				"targets": {
					"node": "current"
				}
			}
		]
	],
...

*Also as an additional note, currently the only place that will have async/await in tests is still in a dev branch yet to be merged in master. https://github.com/thektan/liferay-portal/blob/LPS-96356-fix-frontend-tests/modules/apps/portal-search/portal-search-ranking-web/test/js/components/ResultsRankingForm.js

[wincent]

Thanks @thektan. Would it be possible to do this without creating babel.test.json using the "overrides" feature? Something like:

diff --git a/packages/liferay-npm-scripts/src/config/babel.json b/packages/liferay-npm-scripts/src/config/babel.json
index 94c14b0..64eb93a 100644
--- a/packages/liferay-npm-scripts/src/config/babel.json
+++ b/packages/liferay-npm-scripts/src/config/babel.json
@@ -3,5 +3,16 @@
 	"plugins": [
 		"@babel/proposal-class-properties",
 		"@babel/proposal-object-rest-spread"
+	],
+	"overrides": [
+		{
+			"test": "**/test/*.js",
+			"presets": [
+				"env",
+				{
+					"targets": {"node": "current"}
+				}
+			]
+		}
 	]
 }

(Untested — the "test" glob might not be exactly right — but that's the basic idea.)

[thektan]

@wincent Neat! I used the same glob used in the jest configs.

[wincent]

Nice! Glad it ended up being a minimal change. Let's merge this and we'll see if it breaks all the JS tests in liferay-portal. 😂

[wincent]

@thektan: I rebased your branch on top of current "master" and added one tweak on top (b12b6fc) just to make sure we don't end up depending on untranspiled features that don't exist in liferay-portal's version of Node (v10.15.1) yet. It has async/await, for example, but not public class fields (silly example, I know, as we're unlikely to use those in a test, but you get the idea).