Outdated index files from previous builds break tests. Use t.TempDir() to make
sure a new index file is used.
diff --git a/integration_test/testutil_test.go b/integration_test/testutil_test.go
index 66ebc98..d91635b 100644
--- a/integration_test/testutil_test.go
+++ b/integration_test/testutil_test.go
@@ -277,7 +277,7 @@ func (it *ITest) loadReceipt(path string) index.Receipt {
 // It caches the index tree as in-memory tar after the first run.
 func (it *ITest) initializeIndex() {
 	initIndexOnce.Do(func() {
-		persistentCacheFile := filepath.Join(os.TempDir(), persistentIndexCache)
+		persistentCacheFile := filepath.Join(it.t.TempDir(), persistentIndexCache)
 		fileInfo, err := os.Stat(persistentCacheFile)
 
 		if err == nil && fileInfo.Mode().IsRegular() {