chore: organize test files

packages/webpack5/scripts/jest.mockFiles.ts

@@ -0,0 +1,42 @@
+import dedent from 'ts-dedent';
+
+const mockedFiles: { [path: string]: string } = {};
+
+export function mockFile(path, content) {
+	const unionFS = require('unionfs').default;
+	const Volume = require('memfs').Volume;
+
+	// reset to fs
+	unionFS.reset();
+
+	// add mocked file
+	mockedFiles[path] = dedent(content);
+
+	// create new volume
+	const vol = Volume.fromJSON(mockedFiles, '__jest__');
+
+	// use the new volume
+	unionFS.use(vol as any);
+}
+
+// a virtual mock for package.json
+jest.mock(
+	'__jest__/package.json',
+	() => ({
+		main: 'src/app.js',
+		devDependencies: {
+			typescript: '*',
+		},
+	}),
+	{ virtual: true }
+);
+
+jest.mock('fs', () => {
+	const fs = jest.requireActual('fs');
+	const unionFS = require('unionfs').default;
+	unionFS.reset = () => {
+		unionFS.fss = [fs];
+	};
+
+	return unionFS.use(fs);
+});