go/packages: make packagestest.Export call t.Helper

Change-Id: Ib95ab480899ee14fb8ae841b0210734ecbc0d0d9
Reviewed-on: https://go-review.googlesource.com/c/145698
Run-TryBot: Ian Cottrell <iancottrell@google.com>
Run-TryBot: Michael Matloob <matloob@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Matloob <matloob@golang.org>
diff --git a/go/packages/packagestest/export.go b/go/packages/packagestest/export.go
index a48da61..bed350c 100644
--- a/go/packages/packagestest/export.go
+++ b/go/packages/packagestest/export.go
@@ -94,6 +94,7 @@
 // flag when invoking the test, allowing the temporary directory to be left for
 // debugging tests.
 func Export(t *testing.T, exporter Exporter, modules []Module) *Exported {
+	t.Helper()
 	temp, err := ioutil.TempDir("", strings.Replace(t.Name(), "/", "_", -1))
 	if err != nil {
 		t.Fatal(err)