chore: refactor unit tests

tests/unit/setup/overlay-fs.ts

@@ -0,0 +1,39 @@
+import { vi } from 'vitest';
+
+const fakeFs = new Map<string, string>();
+export function createFakeFile(path: string, content: string) {
+	fakeFs.set(path, content);
+}
+
+export function clearFakeFiles() {
+	fakeFs.clear();
+}
+
+vi.mock(import('node:fs/promises'), async (importOrig) => {
+	const orig = await importOrig();
+	return {
+		...orig,
+		readFile: (path, options) => {
+			const p = path.toString();
+			if (fakeFs.has(p)) {
+				const content = fakeFs.get(p)!;
+				if (typeof options === 'string' || options?.encoding) {
+					return Promise.resolve(content);
+				}
+
+				return Promise.resolve(Buffer.from(content));
+			}
+
+			return orig.readFile.call(this, path, options);
+		},
+
+		access: (path, mode) => {
+			const p = path.toString();
+			if (p === '/var/lib/headplane/' || p === '/var/lib/headplane') {
+				return Promise.resolve();
+			}
+
+			return orig.access.call(this, path, mode);
+		},
+	};
+});