karma-rollup-preprocessor/.babelrc

{
	"presets": [
		[
			"@babel/preset-env",
			{
				"useBuiltIns": "usage",
				"corejs": {
					"version": 3
				},
				"targets": "last 2 versions"
			}
		]
	],
	"plugins": [
		[
			"@babel/plugin-transform-typescript",
			{
				"allowNamespaces": true
			}
		]
	]
}