diff --git a/src/hooks/directory-readme-injector/injector.test.ts b/src/hooks/directory-readme-injector/injector.test.ts
index 775d8a89..932fb77e 100644
--- a/src/hooks/directory-readme-injector/injector.test.ts
+++ b/src/hooks/directory-readme-injector/injector.test.ts
@@ -1,53 +1,67 @@
-import { beforeEach, describe, expect, it, mock } from "bun:test"
+import { afterEach, beforeEach, describe, expect, it, mock } from "bun:test"
+import { mkdirSync, rmSync, writeFileSync } from "node:fs"
+import { tmpdir } from "node:os"
+import { join } from "node:path"
 
-const readFileSyncMock = mock((_: string, __: string) => "# README")
 const findReadmeMdUpMock = mock((_: { startDir: string; rootDir: string }) => [] as string[])
 const resolveFilePathMock = mock((_: string, path: string) => path)
 const loadInjectedPathsMock = mock((_: string) => new Set<string>())
 const saveInjectedPathsMock = mock((_: string, __: Set<string>) => {})
 
-mock.module("node:fs", () => ({
-  readFileSync: readFileSyncMock,
-}))
-
-mock.module("./finder", () => ({
-  findReadmeMdUp: findReadmeMdUpMock,
-  resolveFilePath: resolveFilePathMock,
-}))
-
-mock.module("./storage", () => ({
-  loadInjectedPaths: loadInjectedPathsMock,
-  saveInjectedPaths: saveInjectedPathsMock,
-}))
-
-const { processFilePathForReadmeInjection } = await import("./injector")
-
 describe("processFilePathForReadmeInjection", () => {
+  let testRoot = ""
+
   beforeEach(() => {
-    readFileSyncMock.mockClear()
     findReadmeMdUpMock.mockClear()
     resolveFilePathMock.mockClear()
     loadInjectedPathsMock.mockClear()
     saveInjectedPathsMock.mockClear()
+
+    testRoot = join(
+      tmpdir(),
+      `directory-readme-injector-${Date.now()}-${Math.random().toString(16).slice(2)}`
+    )
+    mkdirSync(testRoot, { recursive: true })
+  })
+
+  afterEach(() => {
+    mock.restore()
+    rmSync(testRoot, { recursive: true, force: true })
   })
 
   it("does not save when all discovered paths are already cached", async () => {
     //#given
     const sessionID = "session-1"
-    const cachedDirectory = "/repo/src"
+    const repoRoot = join(testRoot, "repo")
+    const readmePath = join(repoRoot, "src", "README.md")
+    const cachedDirectory = join(repoRoot, "src")
+    mkdirSync(join(repoRoot, "src"), { recursive: true })
+    writeFileSync(readmePath, "# README")
+
     loadInjectedPathsMock.mockReturnValueOnce(new Set([cachedDirectory]))
-    findReadmeMdUpMock.mockReturnValueOnce(["/repo/src/README.md"])
+    findReadmeMdUpMock.mockReturnValueOnce([readmePath])
 
     const truncator = {
       truncate: mock(async () => ({ result: "trimmed", truncated: false })),
     }
 
+    mock.module("./finder", () => ({
+      findReadmeMdUp: findReadmeMdUpMock,
+      resolveFilePath: resolveFilePathMock,
+    }))
+    mock.module("./storage", () => ({
+      loadInjectedPaths: loadInjectedPathsMock,
+      saveInjectedPaths: saveInjectedPathsMock,
+    }))
+
+    const { processFilePathForReadmeInjection } = await import("./injector")
+
     //#when
     await processFilePathForReadmeInjection({
-      ctx: { directory: "/repo" } as never,
+      ctx: { directory: repoRoot } as never,
       truncator: truncator as never,
       sessionCaches: new Map(),
-      filePath: "/repo/src/file.ts",
+      filePath: join(repoRoot, "src", "file.ts"),
       sessionID,
       output: { title: "Result", output: "", metadata: {} },
     })
@@ -59,19 +73,36 @@ describe("processFilePathForReadmeInjection", () => {
   it("saves when a new path is injected", async () => {
     //#given
     const sessionID = "session-2"
+    const repoRoot = join(testRoot, "repo")
+    const readmePath = join(repoRoot, "src", "README.md")
+    const injectedDirectory = join(repoRoot, "src")
+    mkdirSync(join(repoRoot, "src"), { recursive: true })
+    writeFileSync(readmePath, "# README")
+
     loadInjectedPathsMock.mockReturnValueOnce(new Set())
-    findReadmeMdUpMock.mockReturnValueOnce(["/repo/src/README.md"])
+    findReadmeMdUpMock.mockReturnValueOnce([readmePath])
 
     const truncator = {
       truncate: mock(async () => ({ result: "trimmed", truncated: false })),
     }
 
+    mock.module("./finder", () => ({
+      findReadmeMdUp: findReadmeMdUpMock,
+      resolveFilePath: resolveFilePathMock,
+    }))
+    mock.module("./storage", () => ({
+      loadInjectedPaths: loadInjectedPathsMock,
+      saveInjectedPaths: saveInjectedPathsMock,
+    }))
+
+    const { processFilePathForReadmeInjection } = await import("./injector")
+
     //#when
     await processFilePathForReadmeInjection({
-      ctx: { directory: "/repo" } as never,
+      ctx: { directory: repoRoot } as never,
       truncator: truncator as never,
       sessionCaches: new Map(),
-      filePath: "/repo/src/file.ts",
+      filePath: join(repoRoot, "src", "file.ts"),
       sessionID,
       output: { title: "Result", output: "", metadata: {} },
     })
@@ -80,28 +111,44 @@ describe("processFilePathForReadmeInjection", () => {
     expect(saveInjectedPathsMock).toHaveBeenCalledTimes(1)
     const saveCall = saveInjectedPathsMock.mock.calls[0]
     expect(saveCall[0]).toBe(sessionID)
-    expect((saveCall[1] as Set<string>).has("/repo/src")).toBe(true)
+    expect((saveCall[1] as Set<string>).has(injectedDirectory)).toBe(true)
   })
 
   it("saves once when cached and new paths are mixed", async () => {
     //#given
     const sessionID = "session-3"
-    loadInjectedPathsMock.mockReturnValueOnce(new Set(["/repo/already-cached"]))
-    findReadmeMdUpMock.mockReturnValueOnce([
-      "/repo/already-cached/README.md",
-      "/repo/new-dir/README.md",
-    ])
+    const repoRoot = join(testRoot, "repo")
+    const cachedReadmePath = join(repoRoot, "already-cached", "README.md")
+    const newReadmePath = join(repoRoot, "new-dir", "README.md")
+    mkdirSync(join(repoRoot, "already-cached"), { recursive: true })
+    mkdirSync(join(repoRoot, "new-dir"), { recursive: true })
+    writeFileSync(cachedReadmePath, "# README")
+    writeFileSync(newReadmePath, "# README")
+
+    loadInjectedPathsMock.mockReturnValueOnce(new Set([join(repoRoot, "already-cached")]))
+    findReadmeMdUpMock.mockReturnValueOnce([cachedReadmePath, newReadmePath])
 
     const truncator = {
       truncate: mock(async () => ({ result: "trimmed", truncated: false })),
     }
 
+    mock.module("./finder", () => ({
+      findReadmeMdUp: findReadmeMdUpMock,
+      resolveFilePath: resolveFilePathMock,
+    }))
+    mock.module("./storage", () => ({
+      loadInjectedPaths: loadInjectedPathsMock,
+      saveInjectedPaths: saveInjectedPathsMock,
+    }))
+
+    const { processFilePathForReadmeInjection } = await import("./injector")
+
     //#when
     await processFilePathForReadmeInjection({
-      ctx: { directory: "/repo" } as never,
+      ctx: { directory: repoRoot } as never,
       truncator: truncator as never,
       sessionCaches: new Map(),
-      filePath: "/repo/new-dir/file.ts",
+      filePath: join(repoRoot, "new-dir", "file.ts"),
       sessionID,
       output: { title: "Result", output: "", metadata: {} },
     })
@@ -109,6 +156,6 @@ describe("processFilePathForReadmeInjection", () => {
     //#then
     expect(saveInjectedPathsMock).toHaveBeenCalledTimes(1)
     const saveCall = saveInjectedPathsMock.mock.calls[0]
-    expect((saveCall[1] as Set<string>).has("/repo/new-dir")).toBe(true)
+    expect((saveCall[1] as Set<string>).has(join(repoRoot, "new-dir"))).toBe(true)
   })
 })