From 758b8b6e5d1aa171827759e51847bcc4f2eea7a3 Mon Sep 17 00:00:00 2001
From: Rich Trott <rtrott@gmail.com>
Date: Sun, 9 Apr 2017 10:36:14 -0700
Subject: [PATCH] assert: improve assert.fail() API
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assert.fail() has two possible function signatures, both of which are
not intuitive. It virtually guarantees that people who try to use
assert.fail() without carefully reading the docs will end up using it
incorrectly.

This change maintains backwards compatibility with the two valid uses
(arguments 1 2 and 4 supplied but argument 3 falsy, and argument 3
supplied but arguments 1 2 and 4 all falsy) but also adds the far more
intuitive first-argument-only and first-two-arguments-only
possibilities.

assert.fail('boom');
// AssertionError: boom

assert.fail('a', 'b');
// AssertionError: 'a' != 'b'

PR-URL: https://github.com/nodejs/node/pull/12293
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
---
 doc/api/assert.md                 |  9 ++++++++-
 lib/assert.js                     |  4 ++++
 test/parallel/test-assert-fail.js | 33 +++++++++++++++++++++++++++++++
 3 files changed, 45 insertions(+), 1 deletion(-)
 create mode 100644 test/parallel/test-assert-fail.js

diff --git a/doc/api/assert.md b/doc/api/assert.md
index 925108b8fc..58c3e7c07f 100644
--- a/doc/api/assert.md
+++ b/doc/api/assert.md
@@ -256,6 +256,7 @@ If the values are not equal, an `AssertionError` is thrown with a `message`
 property set equal to the value of the `message` parameter. If the `message`
 parameter is undefined, a default error message is assigned.
 
+## assert.fail(message)
 ## assert.fail(actual, expected, message, operator)
 <!-- YAML
 added: v0.1.21
@@ -263,7 +264,7 @@ added: v0.1.21
 * `actual` {any}
 * `expected` {any}
 * `message` {any}
-* `operator` {string}
+* `operator` {string} (default: '!=')
 
 Throws an `AssertionError`. If `message` is falsy, the error message is set as
 the values of `actual` and `expected` separated by the provided `operator`.
@@ -277,6 +278,12 @@ assert.fail(1, 2, undefined, '>');
 
 assert.fail(1, 2, 'whoops', '>');
 // AssertionError: whoops
+
+assert.fail('boom');
+// AssertionError: boom
+
+assert.fail('a', 'b');
+// AssertionError: 'a' != 'b'
 ```
 
 ## assert.ifError(value)
diff --git a/lib/assert.js b/lib/assert.js
index 303a00e8ae..8e421901a8 100644
--- a/lib/assert.js
+++ b/lib/assert.js
@@ -79,6 +79,10 @@ function getMessage(self) {
 // display purposes.
 
 function fail(actual, expected, message, operator, stackStartFunction) {
+  if (arguments.length === 1)
+    message = actual;
+  if (arguments.length === 2)
+    operator = '!=';
   throw new assert.AssertionError({
     message: message,
     actual: actual,
diff --git a/test/parallel/test-assert-fail.js b/test/parallel/test-assert-fail.js
new file mode 100644
index 0000000000..5a321c6bb3
--- /dev/null
+++ b/test/parallel/test-assert-fail.js
@@ -0,0 +1,33 @@
+'use strict';
+require('../common');
+const assert = require('assert');
+
+// no args
+assert.throws(
+  () => { assert.fail(); },
+  /^AssertionError: undefined undefined undefined$/
+);
+
+// one arg = message
+assert.throws(
+  () => { assert.fail('custom message'); },
+  /^AssertionError: custom message$/
+);
+
+// two args only, operator defaults to '!='
+assert.throws(
+  () => { assert.fail('first', 'second'); },
+  /^AssertionError: 'first' != 'second'$/
+);
+
+// three args
+assert.throws(
+  () => { assert.fail('ignored', 'ignored', 'another custom message'); },
+  /^AssertionError: another custom message$/
+);
+
+// no third arg (but a fourth arg)
+assert.throws(
+  () => { assert.fail('first', 'second', undefined, 'operator'); },
+  /^AssertionError: 'first' operator 'second'$/
+);