feat: Add pretty assert (denoland/deno_std#187)

Original: https://github.com/denoland/deno_std/commit/ddafcc6572b6574eb0566d650e5f9ca9f049a8d6

7 files changed, 1800 insertions, 0 deletions

diff --git a/testing/diff.ts b/testing/diff.ts
new file mode 100644
index 000000000..a1385b88a
--- /dev/null
+++ b/testing/diff.ts
@@ -0,0 +1,198 @@
+// Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
+interface FarthestPoint {
+  y: number;
+  id: number;
+}
+
+export type DiffType = "removed" | "common" | "added";
+
+export interface DiffResult<T> {
+  type: DiffType;
+  value: T;
+}
+
+const REMOVED = 1;
+const COMMON = 2;
+const ADDED = 3;
+
+function createCommon<T>(A: T[], B: T[], reverse?: boolean) {
+  const common = [];
+  if (A.length === 0 || B.length === 0) return [];
+  for (let i = 0; i < Math.min(A.length, B.length); i += 1) {
+    if (
+      A[reverse ? A.length - i - 1 : i] === B[reverse ? B.length - i - 1 : i]
+    ) {
+      common.push(A[reverse ? A.length - i - 1 : i]);
+    } else {
+      return common;
+    }
+  }
+  return common;
+}
+
+export default function diff<T>(A: T[], B: T[]): DiffResult<T>[] {
+  function backTrace<T>(
+    A: T[],
+    B: T[],
+    current: FarthestPoint,
+    swapped: boolean
+  ) {
+    const M = A.length;
+    const N = B.length;
+    const result = [];
+    let a = M - 1;
+    let b = N - 1;
+    let j = routes[current.id];
+    let type = routes[current.id + diffTypesPtrOffset];
+    while (true) {
+      if (!j && !type) break;
+      const prev = j;
+      if (type === REMOVED) {
+        result.unshift({
+          type: (swapped ? "removed" : "added") as DiffType,
+          value: B[b]
+        });
+        b -= 1;
+      } else if (type === ADDED) {
+        result.unshift({
+          type: (swapped ? "added" : "removed") as DiffType,
+          value: A[a]
+        });
+        a -= 1;
+      } else {
+        result.unshift({ type: "common" as DiffType, value: A[a] });
+        a -= 1;
+        b -= 1;
+      }
+      j = routes[prev];
+      type = routes[prev + diffTypesPtrOffset];
+    }
+    return result;
+  }
+
+  function createFP(
+    slide: FarthestPoint,
+    down: FarthestPoint,
+    k: number,
+    M: number,
+    N: number
+  ): FarthestPoint {
+    if (slide && slide.y === -1 && (down && down.y === -1))
+      return { y: 0, id: 0 };
+    if (
+      (down && down.y === -1) ||
+      k === M ||
+      (slide && slide.y) > (down && down.y) + 1
+    ) {
+      const prev = slide.id;
+      ptr++;
+      routes[ptr] = prev;
+      routes[ptr + diffTypesPtrOffset] = ADDED;
+      return { y: slide.y, id: ptr };
+    } else {
+      const prev = down.id;
+      ptr++;
+      routes[ptr] = prev;
+      routes[ptr + diffTypesPtrOffset] = REMOVED;
+      return { y: down.y + 1, id: ptr };
+    }
+  }
+
+  function snake<T>(
+    k: number,
+    slide: FarthestPoint,
+    down: FarthestPoint,
+    offset: number,
+    A: T[],
+    B: T[]
+  ) {
+    const M = A.length;
+    const N = B.length;
+    if (k < -N || M < k) return { y: -1 };
+    const fp = createFP(slide, down, k, M, N);
+    while (fp.y + k < M && fp.y < N && A[fp.y + k] === B[fp.y]) {
+      const prev = fp.id;
+      ptr++;
+      fp.id = ptr;
+      fp.y += 1;
+      routes[ptr] = prev;
+      routes[ptr + diffTypesPtrOffset] = COMMON;
+    }
+    return fp;
+  }
+
+  const prefixCommon = createCommon(A, B);
+  const suffixCommon = createCommon(
+    A.slice(prefixCommon.length),
+    B.slice(prefixCommon.length),
+    true
+  ).reverse();
+  A = suffixCommon.length
+    ? A.slice(prefixCommon.length, -suffixCommon.length)
+    : A.slice(prefixCommon.length);
+  B = suffixCommon.length
+    ? B.slice(prefixCommon.length, -suffixCommon.length)
+    : B.slice(prefixCommon.length);
+  const swapped = B.length > A.length;
+  [A, B] = swapped ? [B, A] : [A, B];
+  const M = A.length;
+  const N = B.length;
+  if (!M && !N && !suffixCommon.length && !prefixCommon.length) return [];
+  if (!N) {
+    return [
+      ...prefixCommon.map(c => ({ type: "common" as DiffType, value: c })),
+      ...A.map(a => ({
+        type: (swapped ? "added" : "removed") as DiffType,
+        value: a
+      })),
+      ...suffixCommon.map(c => ({ type: "common" as DiffType, value: c }))
+    ];
+  }
+  const offset = N;
+  const delta = M - N;
+  const size = M + N + 1;
+  const fp = new Array(size).fill({ y: -1 });
+  // INFO: This buffer is used to save memory and improve performance.
+  //       The first half is used to save route and last half is used to save diff type.
+  //       This is because, when I kept new uint8array area to save type, performance worsened.
+  const routes = new Uint32Array((M * N + size + 1) * 2);
+  const diffTypesPtrOffset = routes.length / 2;
+  let ptr = 0;
+  let p = -1;
+  while (fp[delta + offset].y < N) {
+    p = p + 1;
+    for (let k = -p; k < delta; ++k) {
+      fp[k + offset] = snake(
+        k,
+        fp[k - 1 + offset],
+        fp[k + 1 + offset],
+        offset,
+        A,
+        B
+      );
+    }
+    for (let k = delta + p; k > delta; --k) {
+      fp[k + offset] = snake(
+        k,
+        fp[k - 1 + offset],
+        fp[k + 1 + offset],
+        offset,
+        A,
+        B
+      );
+    }
+    fp[delta + offset] = snake(
+      delta,
+      fp[delta - 1 + offset],
+      fp[delta + 1 + offset],
+      offset,
+      A,
+      B
+    );
+  }
+  return [
+    ...prefixCommon.map(c => ({ type: "common" as DiffType, value: c })),
+    ...backTrace(A, B, fp[delta + offset], swapped),
+    ...suffixCommon.map(c => ({ type: "common" as DiffType, value: c }))
+  ];
+}
diff --git a/testing/diff_test.ts b/testing/diff_test.ts
new file mode 100644
index 000000000..d2259ba35
--- /dev/null
+++ b/testing/diff_test.ts
@@ -0,0 +1,110 @@
+import diff from "./diff.ts";
+import { test, assertEqual } from "./mod.ts";
+
+test({
+  name: "empty",
+  fn() {
+    assertEqual(diff([], []), []);
+  }
+});
+
+test({
+  name: '"a" vs "b"',
+  fn() {
+    assertEqual(diff(["a"], ["b"]), [
+      { type: "removed", value: "a" },
+      { type: "added", value: "b" }
+    ]);
+  }
+});
+
+test({
+  name: '"a" vs "a"',
+  fn() {
+    assertEqual(diff(["a"], ["a"]), [{ type: "common", value: "a" }]);
+  }
+});
+
+test({
+  name: '"a" vs ""',
+  fn() {
+    assertEqual(diff(["a"], []), [{ type: "removed", value: "a" }]);
+  }
+});
+
+test({
+  name: '"" vs "a"',
+  fn() {
+    assertEqual(diff([], ["a"]), [{ type: "added", value: "a" }]);
+  }
+});
+
+test({
+  name: '"a" vs "a, b"',
+  fn() {
+    assertEqual(diff(["a"], ["a", "b"]), [
+      { type: "common", value: "a" },
+      { type: "added", value: "b" }
+    ]);
+  }
+});
+
+test({
+  name: '"strength" vs "string"',
+  fn() {
+    assertEqual(diff(Array.from("strength"), Array.from("string")), [
+      { type: "common", value: "s" },
+      { type: "common", value: "t" },
+      { type: "common", value: "r" },
+      { type: "removed", value: "e" },
+      { type: "added", value: "i" },
+      { type: "common", value: "n" },
+      { type: "common", value: "g" },
+      { type: "removed", value: "t" },
+      { type: "removed", value: "h" }
+    ]);
+  }
+});
+
+test({
+  name: '"strength" vs ""',
+  fn() {
+    assertEqual(diff(Array.from("strength"), Array.from("")), [
+      { type: "removed", value: "s" },
+      { type: "removed", value: "t" },
+      { type: "removed", value: "r" },
+      { type: "removed", value: "e" },
+      { type: "removed", value: "n" },
+      { type: "removed", value: "g" },
+      { type: "removed", value: "t" },
+      { type: "removed", value: "h" }
+    ]);
+  }
+});
+
+test({
+  name: '"" vs "strength"',
+  fn() {
+    assertEqual(diff(Array.from(""), Array.from("strength")), [
+      { type: "added", value: "s" },
+      { type: "added", value: "t" },
+      { type: "added", value: "r" },
+      { type: "added", value: "e" },
+      { type: "added", value: "n" },
+      { type: "added", value: "g" },
+      { type: "added", value: "t" },
+      { type: "added", value: "h" }
+    ]);
+  }
+});
+
+test({
+  name: '"abc", "c" vs "abc", "bcd", "c"',
+  fn() {
+    assertEqual(diff(["abc", "c"], ["abc", "bcd", "c"]), [
+      { type: "common", value: "abc" },
+      { type: "added", value: "bcd" },
+      { type: "common", value: "c" }
+    ]);
+  }
+});
diff --git a/testing/format.ts b/testing/format.ts
new file mode 100644
index 000000000..8434db1c2
--- /dev/null
+++ b/testing/format.ts
@@ -0,0 +1,529 @@
+// This file is ported from pretty-format@24.0.0
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ */
+export type Refs = any[];
+export type Optional<T> = { [K in keyof T]?: T[K] };
+
+export interface Options {
+  callToJSON: boolean;
+  escapeRegex: boolean;
+  escapeString: boolean;
+  indent: number;
+  maxDepth: number;
+  min: boolean;
+  printFunctionName: boolean;
+}
+
+export interface Config {
+  callToJSON: boolean;
+  escapeRegex: boolean;
+  escapeString: boolean;
+  indent: string;
+  maxDepth: number;
+  min: boolean;
+  printFunctionName: boolean;
+  spacingInner: string;
+  spacingOuter: string;
+}
+
+export type Printer = (
+  val: any,
+  config: Config,
+  indentation: string,
+  depth: number,
+  refs: Refs,
+  hasCalledToJSON?: boolean
+) => string;
+
+const toString = Object.prototype.toString;
+const toISOString = Date.prototype.toISOString;
+const errorToString = Error.prototype.toString;
+const regExpToString = RegExp.prototype.toString;
+const symbolToString = Symbol.prototype.toString;
+
+const DEFAULT_OPTIONS: Options = {
+  callToJSON: true,
+  escapeRegex: false,
+  escapeString: true,
+  indent: 2,
+  maxDepth: Infinity,
+  min: false,
+  printFunctionName: true
+};
+
+interface BasicValueOptions {
+  printFunctionName: boolean;
+  escapeRegex: boolean;
+  escapeString: boolean;
+}
+
+/**
+ * Explicitly comparing typeof constructor to function avoids undefined as name
+ * when mock identity-obj-proxy returns the key as the value for any key.
+ */
+const getConstructorName = (val: new (...args: any[]) => any) =>
+  (typeof val.constructor === "function" && val.constructor.name) || "Object";
+
+/* global window */
+/** Is val is equal to global window object? Works even if it does not exist :) */
+const isWindow = (val: any) => typeof window !== "undefined" && val === window;
+
+const SYMBOL_REGEXP = /^Symbol\((.*)\)(.*)$/;
+
+function isToStringedArrayType(toStringed: string): boolean {
+  return (
+    toStringed === "[object Array]" ||
+    toStringed === "[object ArrayBuffer]" ||
+    toStringed === "[object DataView]" ||
+    toStringed === "[object Float32Array]" ||
+    toStringed === "[object Float64Array]" ||
+    toStringed === "[object Int8Array]" ||
+    toStringed === "[object Int16Array]" ||
+    toStringed === "[object Int32Array]" ||
+    toStringed === "[object Uint8Array]" ||
+    toStringed === "[object Uint8ClampedArray]" ||
+    toStringed === "[object Uint16Array]" ||
+    toStringed === "[object Uint32Array]"
+  );
+}
+
+function printNumber(val: number): string {
+  return Object.is(val, -0) ? "-0" : String(val);
+}
+
+function printFunction(val: () => void, printFunctionName: boolean): string {
+  if (!printFunctionName) {
+    return "[Function]";
+  }
+  return "[Function " + (val.name || "anonymous") + "]";
+}
+
+function printSymbol(val: symbol): string {
+  return symbolToString.call(val).replace(SYMBOL_REGEXP, "Symbol($1)");
+}
+
+function printError(val: Error): string {
+  return "[" + errorToString.call(val) + "]";
+}
+
+/**
+ * The first port of call for printing an object, handles most of the
+ * data-types in JS.
+ */
+function printBasicValue(
+  val: any,
+  { printFunctionName, escapeRegex, escapeString }: BasicValueOptions
+): string | null {
+  if (val === true || val === false) {
+    return "" + val;
+  }
+  if (val === undefined) {
+    return "undefined";
+  }
+  if (val === null) {
+    return "null";
+  }
+
+  const typeOf = typeof val;
+
+  if (typeOf === "number") {
+    return printNumber(val);
+  }
+  if (typeOf === "string") {
+    if (escapeString) {
+      return '"' + val.replace(/"|\\/g, "\\$&") + '"';
+    }
+    return '"' + val + '"';
+  }
+  if (typeOf === "function") {
+    return printFunction(val, printFunctionName);
+  }
+  if (typeOf === "symbol") {
+    return printSymbol(val);
+  }
+
+  const toStringed = toString.call(val);
+
+  if (toStringed === "[object WeakMap]") {
+    return "WeakMap {}";
+  }
+  if (toStringed === "[object WeakSet]") {
+    return "WeakSet {}";
+  }
+  if (
+    toStringed === "[object Function]" ||
+    toStringed === "[object GeneratorFunction]"
+  ) {
+    return printFunction(val, printFunctionName);
+  }
+  if (toStringed === "[object Symbol]") {
+    return printSymbol(val);
+  }
+  if (toStringed === "[object Date]") {
+    return isNaN(+val) ? "Date { NaN }" : toISOString.call(val);
+  }
+  if (toStringed === "[object Error]") {
+    return printError(val);
+  }
+  if (toStringed === "[object RegExp]") {
+    if (escapeRegex) {
+      // https://github.com/benjamingr/RegExp.escape/blob/master/polyfill.js
+      return regExpToString.call(val).replace(/[\\^$*+?.()|[\]{}]/g, "\\$&");
+    }
+    return regExpToString.call(val);
+  }
+
+  if (val instanceof Error) {
+    return printError(val);
+  }
+
+  return null;
+}
+
+/**
+ * Handles more complex objects ( such as objects with circular references.
+ * maps and sets etc )
+ */
+function printComplexValue(
+  val: any,
+  config: Config,
+  indentation: string,
+  depth: number,
+  refs: Refs,
+  hasCalledToJSON?: boolean
+): string {
+  if (refs.indexOf(val) !== -1) {
+    return "[Circular]";
+  }
+  refs = refs.slice();
+  refs.push(val);
+
+  const hitMaxDepth = ++depth > config.maxDepth;
+  const { min, callToJSON } = config;
+
+  if (
+    callToJSON &&
+    !hitMaxDepth &&
+    val.toJSON &&
+    typeof val.toJSON === "function" &&
+    !hasCalledToJSON
+  ) {
+    return printer(val.toJSON(), config, indentation, depth, refs, true);
+  }
+
+  const toStringed = toString.call(val);
+  if (toStringed === "[object Arguments]") {
+    return hitMaxDepth
+      ? "[Arguments]"
+      : (min ? "" : "Arguments ") +
+          "[" +
+          printListItems(val, config, indentation, depth, refs, printer) +
+          "]";
+  }
+  if (isToStringedArrayType(toStringed)) {
+    return hitMaxDepth
+      ? "[" + val.constructor.name + "]"
+      : (min ? "" : val.constructor.name + " ") +
+          "[" +
+          printListItems(val, config, indentation, depth, refs, printer) +
+          "]";
+  }
+  if (toStringed === "[object Map]") {
+    return hitMaxDepth
+      ? "[Map]"
+      : "Map {" +
+          printIteratorEntries(
+            val.entries(),
+            config,
+            indentation,
+            depth,
+            refs,
+            printer,
+            " => "
+          ) +
+          "}";
+  }
+  if (toStringed === "[object Set]") {
+    return hitMaxDepth
+      ? "[Set]"
+      : "Set {" +
+          printIteratorValues(
+            val.values(),
+            config,
+            indentation,
+            depth,
+            refs,
+            printer
+          ) +
+          "}";
+  }
+
+  // Avoid failure to serialize global window object in jsdom test environment.
+  // For example, not even relevant if window is prop of React element.
+  return hitMaxDepth || isWindow(val)
+    ? "[" + getConstructorName(val) + "]"
+    : (min ? "" : getConstructorName(val) + " ") +
+        "{" +
+        printObjectProperties(val, config, indentation, depth, refs, printer) +
+        "}";
+}
+
+function printer(
+  val: any,
+  config: Config,
+  indentation: string,
+  depth: number,
+  refs: Refs,
+  hasCalledToJSON?: boolean
+): string {
+  const basicResult = printBasicValue(val, config);
+  if (basicResult !== null) {
+    return basicResult;
+  }
+  return printComplexValue(
+    val,
+    config,
+    indentation,
+    depth,
+    refs,
+    hasCalledToJSON
+  );
+}
+
+const getConfig = (options: Options): Config => ({
+  ...options,
+  indent: options.min ? "" : createIndent(options.indent),
+  spacingInner: options.min ? " " : "\n",
+  spacingOuter: options.min ? "" : "\n"
+});
+
+function createIndent(indent: number): string {
+  return new Array(indent + 1).join(" ");
+}
+
+const getKeysOfEnumerableProperties = (object: {}) => {
+  const keys: Array<string | symbol> = Object.keys(object).sort();
+
+  if (Object.getOwnPropertySymbols) {
+    Object.getOwnPropertySymbols(object).forEach(symbol => {
+      if (Object.getOwnPropertyDescriptor(object, symbol)!.enumerable) {
+        keys.push(symbol);
+      }
+    });
+  }
+
+  return keys;
+};
+
+/**
+ * Return entries (for example, of a map)
+ * with spacing, indentation, and comma
+ * without surrounding punctuation (for example, braces)
+ */
+function printIteratorEntries(
+  iterator: any,
+  config: Config,
+  indentation: string,
+  depth: number,
+  refs: Refs,
+  printer: Printer,
+  // Too bad, so sad that separator for ECMAScript Map has been ' => '
+  // What a distracting diff if you change a data structure to/from
+  // ECMAScript Object or Immutable.Map/OrderedMap which use the default.
+  separator: string = ": "
+): string {
+  let result = "";
+  let current = iterator.next();
+
+  if (!current.done) {
+    result += config.spacingOuter;
+
+    const indentationNext = indentation + config.indent;
+
+    while (!current.done) {
+      const name = printer(
+        current.value[0],
+        config,
+        indentationNext,
+        depth,
+        refs
+      );
+      const value = printer(
+        current.value[1],
+        config,
+        indentationNext,
+        depth,
+        refs
+      );
+
+      result += indentationNext + name + separator + value;
+
+      current = iterator.next();
+
+      if (!current.done) {
+        result += "," + config.spacingInner;
+      } else if (!config.min) {
+        result += ",";
+      }
+    }
+
+    result += config.spacingOuter + indentation;
+  }
+
+  return result;
+}
+
+/**
+ * Return values (for example, of a set)
+ * with spacing, indentation, and comma
+ * without surrounding punctuation (braces or brackets)
+ */
+function printIteratorValues(
+  iterator: Iterator<any>,
+  config: Config,
+  indentation: string,
+  depth: number,
+  refs: Refs,
+  printer: Printer
+): string {
+  let result = "";
+  let current = iterator.next();
+
+  if (!current.done) {
+    result += config.spacingOuter;
+
+    const indentationNext = indentation + config.indent;
+
+    while (!current.done) {
+      result +=
+        indentationNext +
+        printer(current.value, config, indentationNext, depth, refs);
+
+      current = iterator.next();
+
+      if (!current.done) {
+        result += "," + config.spacingInner;
+      } else if (!config.min) {
+        result += ",";
+      }
+    }
+
+    result += config.spacingOuter + indentation;
+  }
+
+  return result;
+}
+
+/**
+ * Return items (for example, of an array)
+ * with spacing, indentation, and comma
+ * without surrounding punctuation (for example, brackets)
+ */
+function printListItems(
+  list: any,
+  config: Config,
+  indentation: string,
+  depth: number,
+  refs: Refs,
+  printer: Printer
+): string {
+  let result = "";
+
+  if (list.length) {
+    result += config.spacingOuter;
+
+    const indentationNext = indentation + config.indent;
+
+    for (let i = 0; i < list.length; i++) {
+      result +=
+        indentationNext +
+        printer(list[i], config, indentationNext, depth, refs);
+
+      if (i < list.length - 1) {
+        result += "," + config.spacingInner;
+      } else if (!config.min) {
+        result += ",";
+      }
+    }
+
+    result += config.spacingOuter + indentation;
+  }
+
+  return result;
+}
+
+/**
+ * Return properties of an object
+ * with spacing, indentation, and comma
+ * without surrounding punctuation (for example, braces)
+ */
+function printObjectProperties(
+  val: {},
+  config: Config,
+  indentation: string,
+  depth: number,
+  refs: Refs,
+  printer: Printer
+): string {
+  let result = "";
+  const keys = getKeysOfEnumerableProperties(val);
+
+  if (keys.length) {
+    result += config.spacingOuter;
+
+    const indentationNext = indentation + config.indent;
+
+    for (let i = 0; i < keys.length; i++) {
+      const key = keys[i];
+      const name = printer(key, config, indentationNext, depth, refs);
+      const value = printer(
+        val[key as keyof typeof val],
+        config,
+        indentationNext,
+        depth,
+        refs
+      );
+
+      result += indentationNext + name + ": " + value;
+
+      if (i < keys.length - 1) {
+        result += "," + config.spacingInner;
+      } else if (!config.min) {
+        result += ",";
+      }
+    }
+
+    result += config.spacingOuter + indentation;
+  }
+
+  return result;
+}
+
+/**
+ * Returns a presentation string of your `val` object
+ * @param val any potential JavaScript object
+ * @param options Custom settings
+ */
+export function format(val: any, options: Optional<Options> = {}): string {
+  const opts = Object.keys(DEFAULT_OPTIONS).reduce(
+    (acc: Options, k: keyof Options) => {
+      const opt = options[k];
+      if (typeof opt === "undefined") {
+        return { ...acc, [k]: DEFAULT_OPTIONS[k] };
+      }
+      return { ...acc, [k]: opt };
+    },
+    {}
+  ) as Options;
+  const basicResult = printBasicValue(val, opts);
+  if (basicResult !== null) {
+    return basicResult;
+  }
+
+  return printComplexValue(val, getConfig(opts), "", 0, []);
+}
diff --git a/testing/format_test.ts b/testing/format_test.ts
new file mode 100644
index 000000000..a07426046
--- /dev/null
+++ b/testing/format_test.ts
@@ -0,0 +1,793 @@
+// This file is ported from pretty-format@24.0.0
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ */
+import { test, assertEqual } from "./mod.ts";
+import { format } from "./format.ts";
+
+function returnArguments(..._args: Array<unknown>) {
+  return arguments;
+}
+
+function MyObject(value: unknown) {
+  // @ts-ignore
+  this.name = value;
+}
+
+class MyArray<T> extends Array<T> {}
+
+const createVal = () => [
+  {
+    id: "8658c1d0-9eda-4a90-95e1-8001e8eb6036",
+    text: "Add alternative serialize API for pretty-format plugins",
+    type: "ADD_TODO"
+  },
+  {
+    id: "8658c1d0-9eda-4a90-95e1-8001e8eb6036",
+    type: "TOGGLE_TODO"
+  }
+];
+
+const createExpected = () =>
+  [
+    "Array [",
+    "  Object {",
+    '    "id": "8658c1d0-9eda-4a90-95e1-8001e8eb6036",',
+    '    "text": "Add alternative serialize API for pretty-format plugins",',
+    '    "type": "ADD_TODO",',
+    "  },",
+    "  Object {",
+    '    "id": "8658c1d0-9eda-4a90-95e1-8001e8eb6036",',
+    '    "type": "TOGGLE_TODO",',
+    "  },",
+    "]"
+  ].join("\n");
+
+test({
+  name: "prints empty arguments",
+  fn() {
+    const val = returnArguments();
+    assertEqual(format(val), "Arguments []");
+  }
+});
+
+test({
+  name: "prints empty arguments",
+  fn() {
+    const val: any[] = [];
+    assertEqual(format(val), "Array []");
+  }
+});
+
+test({
+  name: "prints an array with items",
+  fn() {
+    const val = [1, 2, 3];
+    assertEqual(format(val), "Array [\n  1,\n  2,\n  3,\n]");
+  }
+});
+
+test({
+  name: "prints a empty typed array",
+  fn() {
+    const val = new Uint32Array(0);
+    assertEqual(format(val), "Uint32Array []");
+  }
+});
+
+test({
+  name: "prints a typed array with items",
+  fn() {
+    const val = new Uint32Array(3);
+    assertEqual(format(val), "Uint32Array [\n  0,\n  0,\n  0,\n]");
+  }
+});
+
+test({
+  name: "prints an array buffer",
+  fn() {
+    const val = new ArrayBuffer(3);
+    assertEqual(format(val), "ArrayBuffer []");
+  }
+});
+
+test({
+  name: "prints a nested array",
+  fn() {
+    const val = [[1, 2, 3]];
+    assertEqual(
+      format(val),
+      "Array [\n  Array [\n    1,\n    2,\n    3,\n  ],\n]"
+    );
+  }
+});
+
+test({
+  name: "prints true",
+  fn() {
+    const val = true;
+    assertEqual(format(val), "true");
+  }
+});
+
+test({
+  name: "prints false",
+  fn() {
+    const val = false;
+    assertEqual(format(val), "false");
+  }
+});
+
+test({
+  name: "prints an error",
+  fn() {
+    const val = new Error();
+    assertEqual(format(val), "[Error]");
+  }
+});
+
+test({
+  name: "prints a typed error with a message",
+  fn() {
+    const val = new TypeError("message");
+    assertEqual(format(val), "[TypeError: message]");
+  }
+});
+
+test({
+  name: "prints a function constructor",
+  fn() {
+    // tslint:disable-next-line:function-constructor
+    const val = new Function();
+    assertEqual(format(val), "[Function anonymous]");
+  }
+});
+
+test({
+  name: "prints an anonymous callback function",
+  fn() {
+    let val;
+    function f(cb: () => void) {
+      val = cb;
+    }
+    // tslint:disable-next-line:no-empty
+    f(() => {});
+    assertEqual(format(val), "[Function anonymous]");
+  }
+});
+
+test({
+  name: "prints an anonymous assigned function",
+  fn() {
+    // tslint:disable-next-line:no-empty
+    const val = () => {};
+    const formatted = format(val);
+    assertEqual(
+      formatted === "[Function anonymous]" || formatted === "[Function val]",
+      true
+    );
+  }
+});
+
+test({
+  name: "prints a named function",
+  fn() {
+    // tslint:disable-next-line:no-empty
+    const val = function named() {};
+    assertEqual(format(val), "[Function named]");
+  }
+});
+
+test({
+  name: "prints a named generator function",
+  fn() {
+    const val = function* generate() {
+      yield 1;
+      yield 2;
+      yield 3;
+    };
+    assertEqual(format(val), "[Function generate]");
+  }
+});
+
+test({
+  name: "can customize function names",
+  fn() {
+    // tslint:disable-next-line:no-empty
+    const val = function named() {};
+    assertEqual(
+      format(val, {
+        printFunctionName: false
+      }),
+      "[Function]"
+    );
+  }
+});
+
+test({
+  name: "prints Infinity",
+  fn() {
+    const val = Infinity;
+    assertEqual(format(val), "Infinity");
+  }
+});
+
+test({
+  name: "prints -Infinity",
+  fn() {
+    const val = -Infinity;
+    assertEqual(format(val), "-Infinity");
+  }
+});
+
+test({
+  name: "prints an empty map",
+  fn() {
+    const val = new Map();
+    assertEqual(format(val), "Map {}");
+  }
+});
+
+test({
+  name: "prints a map with values",
+  fn() {
+    const val = new Map();
+    val.set("prop1", "value1");
+    val.set("prop2", "value2");
+    assertEqual(
+      format(val),
+      'Map {\n  "prop1" => "value1",\n  "prop2" => "value2",\n}'
+    );
+  }
+});
+
+test({
+  name: "prints a map with non-string keys",
+  fn() {
+    const val = new Map<any, any>([
+      [false, "boolean"],
+      ["false", "string"],
+      [0, "number"],
+      ["0", "string"],
+      [null, "null"],
+      ["null", "string"],
+      [undefined, "undefined"],
+      ["undefined", "string"],
+      [Symbol("description"), "symbol"],
+      ["Symbol(description)", "string"],
+      [["array", "key"], "array"],
+      [{ key: "value" }, "object"]
+    ]);
+    const expected = [
+      "Map {",
+      '  false => "boolean",',
+      '  "false" => "string",',
+      '  0 => "number",',
+      '  "0" => "string",',
+      '  null => "null",',
+      '  "null" => "string",',
+      '  undefined => "undefined",',
+      '  "undefined" => "string",',
+      '  Symbol(description) => "symbol",',
+      '  "Symbol(description)" => "string",',
+      "  Array [",
+      '    "array",',
+      '    "key",',
+      '  ] => "array",',
+      "  Object {",
+      '    "key": "value",',
+      '  } => "object",',
+      "}"
+    ].join("\n");
+    assertEqual(format(val), expected);
+  }
+});
+
+test({
+  name: "prints NaN",
+  fn() {
+    const val = NaN;
+    assertEqual(format(val), "NaN");
+  }
+});
+
+test({
+  name: "prints null",
+  fn() {
+    const val = null;
+    assertEqual(format(val), "null");
+  }
+});
+
+test({
+  name: "prints a positive number",
+  fn() {
+    const val = 123;
+    assertEqual(format(val), "123");
+  }
+});
+
+test({
+  name: "prints a negative number",
+  fn() {
+    const val = -123;
+    assertEqual(format(val), "-123");
+  }
+});
+
+test({
+  name: "prints zero",
+  fn() {
+    const val = 0;
+    assertEqual(format(val), "0");
+  }
+});
+
+test({
+  name: "prints negative zero",
+  fn() {
+    const val = -0;
+    assertEqual(format(val), "-0");
+  }
+});
+
+test({
+  name: "prints a date",
+  fn() {
+    const val = new Date(10e11);
+    assertEqual(format(val), "2001-09-09T01:46:40.000Z");
+  }
+});
+
+test({
+  name: "prints an invalid date",
+  fn() {
+    const val = new Date(Infinity);
+    assertEqual(format(val), "Date { NaN }");
+  }
+});
+
+test({
+  name: "prints an empty object",
+  fn() {
+    const val = {};
+    assertEqual(format(val), "Object {}");
+  }
+});
+
+test({
+  name: "prints an object with properties",
+  fn() {
+    const val = { prop1: "value1", prop2: "value2" };
+    assertEqual(
+      format(val),
+      'Object {\n  "prop1": "value1",\n  "prop2": "value2",\n}'
+    );
+  }
+});
+
+test({
+  name: "prints an object with properties and symbols",
+  fn() {
+    const val: any = {};
+    val[Symbol("symbol1")] = "value2";
+    val[Symbol("symbol2")] = "value3";
+    val.prop = "value1";
+    assertEqual(
+      format(val),
+      'Object {\n  "prop": "value1",\n  Symbol(symbol1): "value2",\n  Symbol(symbol2): "value3",\n}'
+    );
+  }
+});
+
+test({
+  name:
+    "prints an object without non-enumerable properties which have string key",
+  fn() {
+    const val: any = {
+      enumerable: true
+    };
+    const key = "non-enumerable";
+    Object.defineProperty(val, key, {
+      enumerable: false,
+      value: false
+    });
+    assertEqual(format(val), 'Object {\n  "enumerable": true,\n}');
+  }
+});
+
+test({
+  name:
+    "prints an object without non-enumerable properties which have symbol key",
+  fn() {
+    const val: any = {
+      enumerable: true
+    };
+    const key = Symbol("non-enumerable");
+    Object.defineProperty(val, key, {
+      enumerable: false,
+      value: false
+    });
+    assertEqual(format(val), 'Object {\n  "enumerable": true,\n}');
+  }
+});
+
+test({
+  name: "prints an object with sorted properties",
+  fn() {
+    const val = { b: 1, a: 2 };
+    assertEqual(format(val), 'Object {\n  "a": 2,\n  "b": 1,\n}');
+  }
+});
+
+test({
+  name: "prints regular expressions from constructors",
+  fn() {
+    const val = new RegExp("regexp");
+    assertEqual(format(val), "/regexp/");
+  }
+});
+
+test({
+  name: "prints regular expressions from literals",
+  fn() {
+    const val = /regexp/gi;
+    assertEqual(format(val), "/regexp/gi");
+  }
+});
+
+test({
+  name: "prints regular expressions {escapeRegex: false}",
+  fn() {
+    const val = /regexp\d/gi;
+    assertEqual(format(val), "/regexp\\d/gi");
+  }
+});
+
+test({
+  name: "prints regular expressions {escapeRegex: true}",
+  fn() {
+    const val = /regexp\d/gi;
+    assertEqual(format(val, { escapeRegex: true }), "/regexp\\\\d/gi");
+  }
+});
+
+test({
+  name: "escapes regular expressions nested inside object",
+  fn() {
+    const obj = { test: /regexp\d/gi };
+    assertEqual(
+      format(obj, { escapeRegex: true }),
+      'Object {\n  "test": /regexp\\\\d/gi,\n}'
+    );
+  }
+});
+
+test({
+  name: "prints an empty set",
+  fn() {
+    const val = new Set();
+    assertEqual(format(val), "Set {}");
+  }
+});
+
+test({
+  name: "prints a set with values",
+  fn() {
+    const val = new Set();
+    val.add("value1");
+    val.add("value2");
+    assertEqual(format(val), 'Set {\n  "value1",\n  "value2",\n}');
+  }
+});
+
+test({
+  name: "prints a string",
+  fn() {
+    const val = "string";
+    assertEqual(format(val), '"string"');
+  }
+});
+
+test({
+  name: "prints and escape a string",
+  fn() {
+    const val = "\"'\\";
+    assertEqual(format(val), '"\\"\'\\\\"');
+  }
+});
+
+test({
+  name: "doesn't escape string with {excapeString: false}",
+  fn() {
+    const val = "\"'\\n";
+    assertEqual(format(val, { escapeString: false }), '""\'\\n"');
+  }
+});
+
+test({
+  name: "prints a string with escapes",
+  fn() {
+    assertEqual(format('"-"'), '"\\"-\\""');
+    assertEqual(format("\\ \\\\"), '"\\\\ \\\\\\\\"');
+  }
+});
+
+test({
+  name: "prints a multiline string",
+  fn() {
+    const val = ["line 1", "line 2", "line 3"].join("\n");
+    assertEqual(format(val), '"' + val + '"');
+  }
+});
+
+test({
+  name: "prints a multiline string as value of object property",
+  fn() {
+    const polyline = {
+      props: {
+        id: "J",
+        points: ["0.5,0.460", "0.5,0.875", "0.25,0.875"].join("\n")
+      },
+      type: "polyline"
+    };
+    const val = {
+      props: {
+        children: polyline
+      },
+      type: "svg"
+    };
+    assertEqual(
+      format(val),
+      [
+        "Object {",
+        '  "props": Object {',
+        '    "children": Object {',
+        '      "props": Object {',
+        '        "id": "J",',
+        '        "points": "0.5,0.460',
+        "0.5,0.875",
+        '0.25,0.875",',
+        "      },",
+        '      "type": "polyline",',
+        "    },",
+        "  },",
+        '  "type": "svg",',
+        "}"
+      ].join("\n")
+    );
+  }
+});
+
+test({
+  name: "prints a symbol",
+  fn() {
+    const val = Symbol("symbol");
+    assertEqual(format(val), "Symbol(symbol)");
+  }
+});
+
+test({
+  name: "prints undefined",
+  fn() {
+    const val = undefined;
+    assertEqual(format(val), "undefined");
+  }
+});
+
+test({
+  name: "prints a WeakMap",
+  fn() {
+    const val = new WeakMap();
+    assertEqual(format(val), "WeakMap {}");
+  }
+});
+
+test({
+  name: "prints a WeakSet",
+  fn() {
+    const val = new WeakSet();
+    assertEqual(format(val), "WeakSet {}");
+  }
+});
+
+test({
+  name: "prints deeply nested objects",
+  fn() {
+    const val = { prop: { prop: { prop: "value" } } };
+    assertEqual(
+      format(val),
+      'Object {\n  "prop": Object {\n    "prop": Object {\n      "prop": "value",\n    },\n  },\n}'
+    );
+  }
+});
+
+test({
+  name: "prints circular references",
+  fn() {
+    const val: any = {};
+    val.prop = val;
+    assertEqual(format(val), 'Object {\n  "prop": [Circular],\n}');
+  }
+});
+
+test({
+  name: "prints parallel references",
+  fn() {
+    const inner = {};
+    const val = { prop1: inner, prop2: inner };
+    assertEqual(
+      format(val),
+      'Object {\n  "prop1": Object {},\n  "prop2": Object {},\n}'
+    );
+  }
+});
+
+test({
+  name: "default implicit: 2 spaces",
+  fn() {
+    assertEqual(format(createVal()), createExpected());
+  }
+});
+
+test({
+  name: "default explicit: 2 spaces",
+  fn() {
+    assertEqual(format(createVal(), { indent: 2 }), createExpected());
+  }
+});
+
+// Tests assume that no strings in val contain multiple adjacent spaces!
+test({
+  name: "non-default: 0 spaces",
+  fn() {
+    const indent = 0;
+    assertEqual(
+      format(createVal(), { indent }),
+      createExpected().replace(/ {2}/g, " ".repeat(indent))
+    );
+  }
+});
+
+test({
+  name: "non-default: 4 spaces",
+  fn() {
+    const indent = 4;
+    assertEqual(
+      format(createVal(), { indent }),
+      createExpected().replace(/ {2}/g, " ".repeat(indent))
+    );
+  }
+});
+
+test({
+  name: "can customize the max depth",
+  fn() {
+    const v = [
+      {
+        "arguments empty": returnArguments(),
+        "arguments non-empty": returnArguments("arg"),
+        "array literal empty": [],
+        "array literal non-empty": ["item"],
+        "extended array empty": new MyArray(),
+        "map empty": new Map(),
+        "map non-empty": new Map([["name", "value"]]),
+        "object literal empty": {},
+        "object literal non-empty": { name: "value" },
+        // @ts-ignore
+        "object with constructor": new MyObject("value"),
+        "object without constructor": Object.create(null),
+        "set empty": new Set(),
+        "set non-empty": new Set(["value"])
+      }
+    ];
+    assertEqual(
+      format(v, { maxDepth: 2 }),
+      [
+        "Array [",
+        "  Object {",
+        '    "arguments empty": [Arguments],',
+        '    "arguments non-empty": [Arguments],',
+        '    "array literal empty": [Array],',
+        '    "array literal non-empty": [Array],',
+        '    "extended array empty": [MyArray],',
+        '    "map empty": [Map],',
+        '    "map non-empty": [Map],',
+        '    "object literal empty": [Object],',
+        '    "object literal non-empty": [Object],',
+        '    "object with constructor": [MyObject],',
+        '    "object without constructor": [Object],',
+        '    "set empty": [Set],',
+        '    "set non-empty": [Set],',
+        "  },",
+        "]"
+      ].join("\n")
+    );
+  }
+});
+
+test({
+  name: "prints objects with no constructor",
+  fn() {
+    assertEqual(format(Object.create(null)), "Object {}");
+  }
+});
+
+test({
+  name: "prints identity-obj-proxy with string constructor",
+  fn() {
+    const obj = Object.create(null);
+    obj.constructor = "constructor";
+    const expected = [
+      "Object {", // Object instead of undefined
+      '  "constructor": "constructor",',
+      "}"
+    ].join("\n");
+    assertEqual(format(obj), expected);
+  }
+});
+
+test({
+  name: "calls toJSON and prints its return value",
+  fn() {
+    assertEqual(
+      format({
+        toJSON: () => ({ value: false }),
+        value: true
+      }),
+      'Object {\n  "value": false,\n}'
+    );
+  }
+});
+
+test({
+  name: "calls toJSON and prints an internal representation.",
+  fn() {
+    assertEqual(
+      format({
+        toJSON: () => "[Internal Object]",
+        value: true
+      }),
+      '"[Internal Object]"'
+    );
+  }
+});
+
+test({
+  name: "calls toJSON only on functions",
+  fn() {
+    assertEqual(
+      format({
+        toJSON: false,
+        value: true
+      }),
+      'Object {\n  "toJSON": false,\n  "value": true,\n}'
+    );
+  }
+});
+
+test({
+  name: "does not call toJSON recursively",
+  fn() {
+    assertEqual(
+      format({
+        toJSON: () => ({ toJSON: () => ({ value: true }) }),
+        value: false
+      }),
+      'Object {\n  "toJSON": [Function toJSON],\n}'
+    );
+  }
+});
+
+test({
+  name: "calls toJSON on Sets",
+  fn() {
+    const set = new Set([1]);
+    (set as any).toJSON = () => "map";
+    assertEqual(format(set), '"map"');
+  }
+});
diff --git a/testing/pretty.ts b/testing/pretty.ts
new file mode 100644
index 000000000..aa90f2469
--- /dev/null
+++ b/testing/pretty.ts
@@ -0,0 +1,75 @@
+// Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
+
+import { equal } from "./mod.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]";
+
+function createStr(v: unknown): string {
+  try {
+    return format(v);
+  } catch (e) {
+    return red(CAN_NOT_DISPLAY);
+  }
+}
+
+function createColor(diffType: DiffType) {
+  switch (diffType) {
+    case "added":
+      return (s: string) => green(bold(s));
+    case "removed":
+      return (s: string) => red(bold(s));
+    default:
+      return white;
+  }
+}
+
+function createSign(diffType: DiffType) {
+  switch (diffType) {
+    case "added":
+      return "+   ";
+    case "removed":
+      return "-   ";
+    default:
+      return "    ";
+  }
+}
+
+function buildMessage(diffResult: ReadonlyArray<DiffResult<string>>) {
+  const messages = [];
+  messages.push("");
+  messages.push("");
+  messages.push(
+    `    ${gray(bold("[Diff]"))} ${red(bold("Left"))} / ${green(bold("Right"))}`
+  );
+  messages.push("");
+  messages.push("");
+  diffResult.forEach((result: DiffResult<string>) => {
+    const c = createColor(result.type);
+    messages.push(c(`${createSign(result.type)}${result.value}`));
+  });
+  messages.push("");
+
+  return messages;
+}
+
+export function assertEqual(actual: unknown, expected: unknown) {
+  if (equal(actual, expected)) {
+    return;
+  }
+  let message = "";
+  const actualString = createStr(actual);
+  const expectedString = createStr(expected);
+  try {
+    const diffResult = diff(
+      actualString.split("\n"),
+      expectedString.split("\n")
+    );
+    message = buildMessage(diffResult).join("\n");
+  } catch (e) {
+    message = `\n${red(CAN_NOT_DISPLAY)} + \n\n`;
+  }
+  throw new Error(message);
+}
diff --git a/testing/pretty_test.ts b/testing/pretty_test.ts
new file mode 100644
index 000000000..f3b087aff
--- /dev/null
+++ b/testing/pretty_test.ts
@@ -0,0 +1,92 @@
+// Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
+
+import { test, assert } from "./mod.ts";
+import { red, green, white, gray, bold } from "../colors/mod.ts";
+import { assertEqual } from "./pretty.ts";
+
+const createHeader = () => [
+  "",
+  "",
+  `    ${gray(bold("[Diff]"))} ${red(bold("Left"))} / ${green(bold("Right"))}`,
+  "",
+  ""
+];
+
+const added = (s: string) => green(bold(s));
+const removed = (s: string) => red(bold(s));
+
+test({
+  name: "pass case",
+  fn() {
+    assertEqual({ a: 10 }, { a: 10 });
+    assertEqual(true, true);
+    assertEqual(10, 10);
+    assertEqual("abc", "abc");
+    assertEqual({ a: 10, b: { c: "1" } }, { a: 10, b: { c: "1" } });
+  }
+});
+
+test({
+  name: "failed with number",
+  fn() {
+    assert.throws(
+      () => assertEqual(1, 2),
+      Error,
+      [...createHeader(), removed(`-   1`), added(`+   2`), ""].join("\n")
+    );
+  }
+});
+
+test({
+  name: "failed with number vs string",
+  fn() {
+    assert.throws(
+      () => assertEqual(1, "1"),
+      Error,
+      [...createHeader(), removed(`-   1`), added(`+   "1"`)].join("\n")
+    );
+  }
+});
+
+test({
+  name: "failed with array",
+  fn() {
+    assert.throws(
+      () => assertEqual([1, "2", 3], ["1", "2", 3]),
+      Error,
+      [
+        ...createHeader(),
+        white("    Array ["),
+        removed(`-     1,`),
+        added(`+     "1",`),
+        white('      "2",'),
+        white("      3,"),
+        white("    ]"),
+        ""
+      ].join("\n")
+    );
+  }
+});
+
+test({
+  name: "failed with object",
+  fn() {
+    assert.throws(
+      () => assertEqual({ a: 1, b: "2", c: 3 }, { a: 1, b: 2, c: [3] }),
+      Error,
+      [
+        ...createHeader(),
+        white("    Object {"),
+        white(`      "a": 1,`),
+        added(`+     "b": 2,`),
+        added(`+     "c": Array [`),
+        added(`+       3,`),
+        added(`+     ],`),
+        removed(`-     "b": "2",`),
+        removed(`-     "c": 3,`),
+        white("    }"),
+        ""
+      ].join("\n")
+    );
+  }
+});
diff --git a/testing/test.ts b/testing/test.ts
index a27ffb263..8c780fdf1 100644
--- a/testing/test.ts
+++ b/testing/test.ts
@@ -1,6 +1,9 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
 
 import { test, assert, assertEqual, equal } from "./mod.ts";
+import "./format_test.ts";
+import "./diff_test.ts";
+import "./pretty_test.ts";
 
 test(function testingEqual() {
   assert(equal("world", "world"));