1 files changed, 88 insertions, 0 deletions
diff --git a/testing/asserts_test.ts b/testing/asserts_test.ts
index e4f05f166..ba07b3a83 100644
--- a/testing/asserts_test.ts
+++ b/testing/asserts_test.ts
@@ -15,6 +15,7 @@ import {
   unreachable
 } from "./asserts.ts";
 import { test } from "./mod.ts";
+import { red, green, white, gray, bold } from "../colors/mod.ts";
 
 test(function testingEqual(): void {
   assert(equal("world", "world"));
@@ -163,3 +164,90 @@ test(function testingAssertFail(): void {
     "Failed assertion: foo"
   );
 });
+
+const createHeader = (): string[] => [
+  "",
+  "",
+  `    ${gray(bold("[Diff]"))} ${red(bold("Left"))} / ${green(bold("Right"))}`,
+  "",
+  ""
+];
+
+const added: (s: string) => string = (s: string): string => green(bold(s));
+const removed: (s: string) => string = (s: string): string => red(bold(s));
+
+test({
+  name: "pass case",
+  fn(): void {
+    assertEquals({ a: 10 }, { a: 10 });
+    assertEquals(true, true);
+    assertEquals(10, 10);
+    assertEquals("abc", "abc");
+    assertEquals({ a: 10, b: { c: "1" } }, { a: 10, b: { c: "1" } });
+  }
+});
+
+test({
+  name: "failed with number",
+  fn(): void {
+    assertThrows(
+      (): void => assertEquals(1, 2),
+      AssertionError,
+      [...createHeader(), removed(`-   1`), added(`+   2`), ""].join("\n")
+    );
+  }
+});
+
+test({
+  name: "failed with number vs string",
+  fn(): void {
+    assertThrows(
+      (): void => assertEquals(1, "1"),
+      AssertionError,
+      [...createHeader(), removed(`-   1`), added(`+   "1"`)].join("\n")
+    );
+  }
+});
+
+test({
+  name: "failed with array",
+  fn(): void {
+    assertThrows(
+      (): void => assertEquals([1, "2", 3], ["1", "2", 3]),
+      AssertionError,
+      [
+        ...createHeader(),
+        white("    Array ["),
+        removed(`-     1,`),
+        added(`+     "1",`),
+        white('      "2",'),
+        white("      3,"),
+        white("    ]"),
+        ""
+      ].join("\n")
+    );
+  }
+});
+
+test({
+  name: "failed with object",
+  fn(): void {
+    assertThrows(
+      (): void => assertEquals({ a: 1, b: "2", c: 3 }, { a: 1, b: 2, c: [3] }),
+      AssertionError,
+      [
+        ...createHeader(),
+        white("    Object {"),
+        white(`      "a": 1,`),
+        added(`+     "b": 2,`),
+        added(`+     "c": Array [`),
+        added(`+       3,`),
+        added(`+     ],`),
+        removed(`-     "b": "2",`),
+        removed(`-     "c": 3,`),
+        white("    }"),
+        ""
+      ].join("\n")
+    );
+  }
+});