feat: add vitest, vite, move to tdd

tests/helpers/InMemoryFileSystem.ts

@@ -0,0 +1,42 @@
+import { IFileSystem } from "@/ports";
+
+export class InMemoryFileSystem implements IFileSystem {
+	private files = new Map<string, string>();
+
+	reset(): void {
+		this.files.clear();
+	}
+
+	async readFile(path: string): Promise<string> {
+		const content = this.files.get(path);
+		if (content === undefined) {
+			throw new Error(`ENOENT: no such file: ${path}`);
+		}
+		return content;
+	}
+
+	async writeFile(path: string, content: string): Promise<void> {
+		this.files.set(path, content);
+	}
+
+	async deleteFile(path: string): Promise<void> {
+		this.files.delete(path);
+	}
+
+	async readdir(path: string): Promise<string[]> {
+		const prefix = path.endsWith("/") || path.endsWith("\\") ? path : path + "/";
+		const seen = new Set<string>();
+		for (const key of this.files.keys()) {
+			if (key.startsWith(prefix)) {
+				const relative = key.slice(prefix.length);
+				const top = relative.split(/[/\\]/)[0];
+				if (top) seen.add(top);
+			}
+		}
+		return [...seen];
+	}
+
+	async mkdir(_path: string): Promise<void> {
+		// no-op for in-memory
+	}
+}