diff --git a/src/agents/skills-install.download.test.ts b/src/agents/skills-install.download.test.ts
index 918da9c661d..fe93bebedd1 100644
--- a/src/agents/skills-install.download.test.ts
+++ b/src/agents/skills-install.download.test.ts
@@ -27,37 +27,49 @@ vi.mock("../infra/fs-pinned-write-helper.js", async () => {
   const fs = await import("node:fs/promises");
   const path = await import("node:path");
   const { pipeline } = await import("node:stream/promises");
+
+  type PinnedWriteParams = {
+    rootPath: string;
+    relativeParentPath: string;
+    basename: string;
+    mkdir: boolean;
+    mode: number;
+    input:
+      | { kind: "buffer"; data: string | Buffer; encoding?: BufferEncoding }
+      | { kind: "stream"; stream: NodeJS.ReadableStream };
+  };
+
+  async function resolveParentPath(params: PinnedWriteParams): Promise<string> {
+    const parentPath = params.relativeParentPath
+      ? path.join(params.rootPath, ...params.relativeParentPath.split("/"))
+      : params.rootPath;
+    if (params.mkdir) {
+      await fs.mkdir(parentPath, { recursive: true });
+    }
+    return parentPath;
+  }
+
+  async function writePinnedTarget(params: PinnedWriteParams, targetPath: string) {
+    if (params.input.kind === "buffer") {
+      await fs.writeFile(targetPath, params.input.data, {
+        encoding: params.input.encoding,
+        mode: params.mode,
+      });
+      return;
+    }
+    const handle = await fs.open(targetPath, "w", params.mode);
+    try {
+      await pipeline(params.input.stream, handle.createWriteStream());
+    } finally {
+      await handle.close().catch(() => undefined);
+    }
+  }
+
   return {
-    runPinnedWriteHelper: async (params: {
-      rootPath: string;
-      relativeParentPath: string;
-      basename: string;
-      mkdir: boolean;
-      mode: number;
-      input:
-        | { kind: "buffer"; data: string | Buffer; encoding?: BufferEncoding }
-        | { kind: "stream"; stream: NodeJS.ReadableStream };
-    }) => {
-      const parentPath = params.relativeParentPath
-        ? path.join(params.rootPath, ...params.relativeParentPath.split("/"))
-        : params.rootPath;
-      if (params.mkdir) {
-        await fs.mkdir(parentPath, { recursive: true });
-      }
+    runPinnedWriteHelper: async (params: PinnedWriteParams) => {
+      const parentPath = await resolveParentPath(params);
       const targetPath = path.join(parentPath, params.basename);
-      if (params.input.kind === "buffer") {
-        await fs.writeFile(targetPath, params.input.data, {
-          encoding: params.input.encoding,
-          mode: params.mode,
-        });
-      } else {
-        const handle = await fs.open(targetPath, "w", params.mode);
-        try {
-          await pipeline(params.input.stream, handle.createWriteStream());
-        } finally {
-          await handle.close().catch(() => undefined);
-        }
-      }
+      await writePinnedTarget(params, targetPath);
       const stat = await fs.stat(targetPath);
       return { dev: stat.dev, ino: stat.ino };
     },