diff --git a/testing/diff.ts b/testing/_diff.ts
similarity index 98%
rename from testing/diff.ts
rename to testing/_diff.ts
index 3a9eca4bba1c..5c84e891fe3f 100644
--- a/testing/diff.ts
+++ b/testing/_diff.ts
@@ -36,7 +36,7 @@ function createCommon<T>(A: T[], B: T[], reverse?: boolean): T[] {
   return common;
 }
 
-export default function diff<T>(A: T[], B: T[]): Array<DiffResult<T>> {
+export function diff<T>(A: T[], B: T[]): Array<DiffResult<T>> {
   const prefixCommon = createCommon(A, B);
   const suffixCommon = createCommon(
     A.slice(prefixCommon.length),
diff --git a/testing/diff_test.ts b/testing/_diff_test.ts
similarity index 98%
rename from testing/diff_test.ts
rename to testing/_diff_test.ts
index 33752d89fcc8..211a34c3479b 100644
--- a/testing/diff_test.ts
+++ b/testing/_diff_test.ts
@@ -1,5 +1,5 @@
 // Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
-import diff from "./diff.ts";
+import { diff } from "./_diff.ts";
 import { assertEquals } from "../testing/asserts.ts";
 
 Deno.test({
diff --git a/testing/asserts.ts b/testing/asserts.ts
index 889a622fd923..f93e043dc668 100644
--- a/testing/asserts.ts
+++ b/testing/asserts.ts
@@ -3,7 +3,7 @@
  * for AssertionError messages in browsers. */
 
 import { bold, gray, green, red, stripColor, white } from "../fmt/colors.ts";
-import diff, { DiffResult, DiffType } from "./diff.ts";
+import { diff, DiffResult, DiffType } from "./_diff.ts";
 
 const CAN_NOT_DISPLAY = "[Cannot display]";