Use a constant for the testdata directory
diff --git a/diffmatchpatch/benchutil_test.go b/diffmatchpatch/benchutil_test.go
index 85f273b..b8e404d 100644
--- a/diffmatchpatch/benchutil_test.go
+++ b/diffmatchpatch/benchutil_test.go
@@ -12,12 +12,14 @@
 	"io/ioutil"
 )
 
+const testdataPath = "../testdata/"
+
 func speedtestTexts() (s1 string, s2 string) {
-	d1, err := ioutil.ReadFile("../testdata/speedtest1.txt")
+	d1, err := ioutil.ReadFile(testdataPath + "speedtest1.txt")
 	if err != nil {
 		panic(err)
 	}
-	d2, err := ioutil.ReadFile("../testdata/speedtest2.txt")
+	d2, err := ioutil.ReadFile(testdataPath + "speedtest2.txt")
 	if err != nil {
 		panic(err)
 	}