test: dedupe fixtures and test harness setup

src/test-utils/fixture-suite.ts

@@ -0,0 +1,29 @@
+import fs from "node:fs/promises";
+import os from "node:os";
+import path from "node:path";
+
+export function createFixtureSuite(rootPrefix: string) {
+  let fixtureRoot = "";
+  let fixtureCount = 0;
+
+  return {
+    async setup(): Promise<void> {
+      fixtureRoot = await fs.mkdtemp(path.join(os.tmpdir(), rootPrefix));
+    },
+    async cleanup(): Promise<void> {
+      if (!fixtureRoot) {
+        return;
+      }
+      await fs.rm(fixtureRoot, { recursive: true, force: true });
+      fixtureRoot = "";
+    },
+    async createCaseDir(prefix: string): Promise<string> {
+      if (!fixtureRoot) {
+        throw new Error("Fixture suite not initialized");
+      }
+      const dir = path.join(fixtureRoot, `${prefix}-${fixtureCount++}`);
+      await fs.mkdir(dir, { recursive: true });
+      return dir;
+    },
+  };
+}