diff --git a/src/app/api/v1/purchase-orders/[id]/attachments/[filename]/route.test.ts b/src/app/api/v1/purchase-orders/[id]/attachments/[filename]/route.test.ts
new file mode 100644
index 0000000..8a0d44f
--- /dev/null
+++ b/src/app/api/v1/purchase-orders/[id]/attachments/[filename]/route.test.ts
@@ -0,0 +1,66 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+
+const getOneMock = vi.fn();
+const updateMock = vi.fn();
+
+vi.mock("@/lib/server/pocketbase-admin", () => ({
+  getAdminPocketBase: vi.fn().mockResolvedValue({
+    collection: () => ({
+      getOne: getOneMock,
+      update: updateMock,
+    }),
+  }),
+}));
+
+import { DELETE } from "./route";
+
+describe("DELETE /api/v1/purchase-orders/[id]/attachments/[filename]", () => {
+  beforeEach(() => {
+    getOneMock.mockReset();
+    updateMock.mockReset();
+  });
+
+  afterEach(() => {
+    vi.clearAllMocks();
+  });
+
+  it("removes the matching token from additional_attachments", async () => {
+    getOneMock.mockResolvedValueOnce({
+      id: "po-1",
+      additional_attachments: ["keep-me.pdf", "delete-me.pdf"],
+    });
+    updateMock.mockResolvedValueOnce({});
+
+    const res = await DELETE(
+      new Request(
+        "http://localhost/api/v1/purchase-orders/po-1/attachments/delete-me.pdf",
+        { method: "DELETE" },
+      ) as any,
+      { params: Promise.resolve({ id: "po-1", filename: "delete-me.pdf" }) },
+    );
+
+    expect(res.status).toBe(200);
+    expect(updateMock).toHaveBeenCalledTimes(1);
+    expect(updateMock.mock.calls[0][1]).toEqual({
+      additional_attachments: ["keep-me.pdf"],
+    });
+  });
+
+  it("returns 404 when the token is not in the array", async () => {
+    getOneMock.mockResolvedValueOnce({
+      id: "po-1",
+      additional_attachments: ["only-this.pdf"],
+    });
+
+    const res = await DELETE(
+      new Request(
+        "http://localhost/api/v1/purchase-orders/po-1/attachments/other.pdf",
+        { method: "DELETE" },
+      ) as any,
+      { params: Promise.resolve({ id: "po-1", filename: "other.pdf" }) },
+    );
+
+    expect(res.status).toBe(404);
+    expect(updateMock).not.toHaveBeenCalled();
+  });
+});