Add check of error in int slice test

int_slice_test.go

diff --git a/int_slice_test.go b/int_slice_test.go
index 5f2eee6..745aecb 100644
--- a/int_slice_test.go
+++ b/int_slice_test.go
@@ -60,6 +60,9 @@
 		}
 	}
 	getIS, err := f.GetIntSlice("is")
+	if err != nil {
+		t.Fatalf("got error: %v", err)
+	}
 	for i, v := range getIS {
 		d, err := strconv.Atoi(vals[i])
 		if err != nil {