1 files changed, 74 insertions, 2 deletions
diff --git a/testing/asserts.ts b/testing/asserts.ts
index 904a4a966..56480c95b 100644
--- a/testing/asserts.ts
+++ b/testing/asserts.ts
@@ -1,5 +1,9 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
-import { assertEquals as prettyAssertEqual } from "./pretty.ts";
+import { red, green, white, gray, bold } from "../colors/mod.ts";
+import diff, { DiffType, DiffResult } from "./diff.ts";
+import { format } from "./format.ts";
+
+const CAN_NOT_DISPLAY = "[Cannot display]";
 
 interface Constructor {
   // eslint-disable-next-line @typescript-eslint/no-explicit-any
@@ -13,6 +17,56 @@ export class AssertionError extends Error {
   }
 }
 
+function createStr(v: unknown): string {
+  try {
+    return format(v);
+  } catch (e) {
+    return red(CAN_NOT_DISPLAY);
+  }
+}
+
+function createColor(diffType: DiffType): (s: string) => string {
+  switch (diffType) {
+    case DiffType.added:
+      return (s: string): string => green(bold(s));
+    case DiffType.removed:
+      return (s: string): string => red(bold(s));
+    default:
+      return white;
+  }
+}
+
+function createSign(diffType: DiffType): string {
+  switch (diffType) {
+    case DiffType.added:
+      return "+   ";
+    case DiffType.removed:
+      return "-   ";
+    default:
+      return "    ";
+  }
+}
+
+function buildMessage(diffResult: ReadonlyArray<DiffResult<string>>): string[] {
+  const messages: string[] = [];
+  messages.push("");
+  messages.push("");
+  messages.push(
+    `    ${gray(bold("[Diff]"))} ${red(bold("Left"))} / ${green(bold("Right"))}`
+  );
+  messages.push("");
+  messages.push("");
+  diffResult.forEach(
+    (result: DiffResult<string>): void => {
+      const c = createColor(result.type);
+      messages.push(c(`${createSign(result.type)}${result.value}`));
+    }
+  );
+  messages.push("");
+
+  return messages;
+}
+
 export function equal(c: unknown, d: unknown): boolean {
   const seen = new Map();
   return (function compare(a: unknown, b: unknown): boolean {
@@ -77,7 +131,25 @@ export function assertEquals(
   expected: unknown,
   msg?: string
 ): void {
-  prettyAssertEqual(actual, expected, msg);
+  if (equal(actual, expected)) {
+    return;
+  }
+  let message = "";
+  const actualString = createStr(actual);
+  const expectedString = createStr(expected);
+  try {
+    const diffResult = diff(
+      actualString.split("\n"),
+      expectedString.split("\n")
+    );
+    message = buildMessage(diffResult).join("\n");
+  } catch (e) {
+    message = `\n${red(CAN_NOT_DISPLAY)} + \n\n`;
+  }
+  if (msg) {
+    message = msg;
+  }
+  throw new AssertionError(message);
 }
 
 /**