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

Original: ddafcc6572

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")
+    );
+  }
+});