assert: multiple improvements

1) Switched + / - and red / green in diffs. It seems like that style
   is more natural to most people.

2) Short primitives do not use the diff anymore. Especially short
   numbers can be read well like 1 !== 2. Cases that can not be
   displayed like that (e.g., -0 and +0) use the regular diff output.

3) Improved error descriptions. It was not always clear what the
   messages stood for. That should now be resolved.

4) Added a position indicator for single lines in case a tty is used
   and the line is shorter than the visual columns.

5) Color detection is now done by checking stderr instead of stdout.

PR-URL: #21628
Reviewed-By: Michaël Zasso <[email protected]>
Reviewed-By: Matteo Collina <[email protected]>
Reviewed-By: Anna Henningsen <[email protected]>
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Vse Mozhet Byt <[email protected]>

doc/api/assert.md

@@ -108,15 +108,15 @@ Example error diff:
 const assert = require('assert').strict;
 
 assert.deepEqual([[[1, 2, 3]], 4, 5], [[[1, 2, '3']], 4, 5]);
-// AssertionError: Input A expected to strictly deep-equal input B:
-// + expected - actual ... Lines skipped
+// AssertionError: Expected inputs to be strictly deep-equal:
+// + actual - expected ... Lines skipped
 //
 //   [
 //     [
 // ...
 //       2,
-// -     3
-// +     '3'
+// +     3
+// -     '3'
 //     ],
 // ...
 //     5
@@ -315,11 +315,12 @@ const assert = require('assert').strict;
 
 // This fails because 1 !== '1'.
 assert.deepStrictEqual({ a: 1 }, { a: '1' });
-// AssertionError: Input A expected to strictly deep-equal input B:
-// + expected - actual
+// AssertionError: Expected inputs to be strictly deep-equal:
+// + actual - expected
+//
 //   {
-// -   a: 1
-// +   a: '1'
+// +   a: 1
+// -   a: '1'
 //   }
 
 // The following objects don't have own properties
@@ -330,27 +331,30 @@ Object.setPrototypeOf(fakeDate, Date.prototype);
 
 // Different [[Prototype]]:
 assert.deepStrictEqual(object, fakeDate);
-// AssertionError: Input A expected to strictly deep-equal input B:
-// + expected - actual
-// - {}
-// + Date {}
+// AssertionError: Expected inputs to be strictly deep-equal:
+// + actual - expected
+//
+// + {}
+// - Date {}
 
 // Different type tags:
 assert.deepStrictEqual(date, fakeDate);
-// AssertionError: Input A expected to strictly deep-equal input B:
-// + expected - actual
-// - 2018-04-26T00:49:08.604Z
-// + Date {}
+// AssertionError: Expected inputs to be strictly deep-equal:
+// + actual - expected
+//
+// + 2018-04-26T00:49:08.604Z
+// - Date {}
 
 assert.deepStrictEqual(NaN, NaN);
 // OK, because of the SameValue comparison
 
 // Different unwrapped numbers:
 assert.deepStrictEqual(new Number(1), new Number(2));
-// AssertionError: Input A expected to strictly deep-equal input B:
-// + expected - actual
-// - [Number: 1]
-// + [Number: 2]
+// AssertionError: Expected inputs to be strictly deep-equal:
+// + actual - expected
+//
+// + [Number: 1]
+// - [Number: 2]
 
 assert.deepStrictEqual(new String('foo'), Object('foo'));
 // OK because the object and the string are identical when unwrapped.
@@ -360,17 +364,20 @@ assert.deepStrictEqual(-0, -0);
 
 // Different zeros using the SameValue Comparison:
 assert.deepStrictEqual(0, -0);
-// AssertionError: Input A expected to strictly deep-equal input B:
-// + expected - actual
-// - 0
-// + -0
+// AssertionError: Expected inputs to be strictly deep-equal:
+// + actual - expected
+//
+// + 0
+// - -0
 
 const symbol1 = Symbol();
 const symbol2 = Symbol();
 assert.deepStrictEqual({ [symbol1]: 1 }, { [symbol1]: 1 });
 // OK, because it is the same symbol on both objects.
+
 assert.deepStrictEqual({ [symbol1]: 1 }, { [symbol2]: 1 });
-// AssertionError [ERR_ASSERTION]: Input objects not identical:
+// AssertionError [ERR_ASSERTION]: Inputs identical but not reference equal:
+//
 // {
 //   [Symbol()]: 1
 // }
@@ -385,12 +392,13 @@ assert.deepStrictEqual(weakMap1, weakMap2);
 
 // Fails because weakMap3 has a property that weakMap1 does not contain:
 assert.deepStrictEqual(weakMap1, weakMap3);
-// AssertionError: Input A expected to strictly deep-equal input B:
-// + expected - actual
+// AssertionError: Expected inputs to be strictly deep-equal:
+// + actual - expected
+//
 //   WeakMap {
-// -   [items unknown]
-// +   [items unknown],
-// +   unequal: true
+// +   [items unknown]
+// -   [items unknown],
+// -   unequal: true
 //   }
 ```
 
@@ -875,7 +883,9 @@ assert.notStrictEqual(1, 2);
 // OK
 
 assert.notStrictEqual(1, 1);
-// AssertionError [ERR_ASSERTION]: Identical input passed to notStrictEqual: 1
+// AssertionError [ERR_ASSERTION]: Expected "actual" to be strictly unequal to:
+//
+// 1
 
 assert.notStrictEqual(1, '1');
 // OK
@@ -1031,19 +1041,20 @@ determined by the [SameValue Comparison][].
 const assert = require('assert').strict;
 
 assert.strictEqual(1, 2);
-// AssertionError [ERR_ASSERTION]: Input A expected to strictly equal input B:
-// + expected - actual
-// - 1
-// + 2
+// AssertionError [ERR_ASSERTION]: Expected inputs to be strictly equal:
+//
+// 1 !== 2
 
 assert.strictEqual(1, 1);
 // OK
 
-assert.strictEqual(1, '1');
-// AssertionError [ERR_ASSERTION]: Input A expected to strictly equal input B:
-// + expected - actual
-// - 1
-// + '1'
+assert.strictEqual('Hello foobar', 'Hello World!');
+// AssertionError [ERR_ASSERTION]: Expected inputs to be strictly equal:
+// + actual - expected
+//
+// + 'Hello foobar'
+// - 'Hello World!'
+//          ^
 ```
 
 If the values are not strictly equal, an `AssertionError` is thrown with a
@@ -1211,20 +1222,21 @@ function notThrowing() {}
 assert.throws(throwingFirst, 'Second');
 // In the next example the message has no benefit over the message from the
 // error and since it is not clear if the user intended to actually match
-// against the error message, Node.js thrown an `ERR_AMBIGUOUS_ARGUMENT` error.
+// against the error message, Node.js throws an `ERR_AMBIGUOUS_ARGUMENT` error.
 assert.throws(throwingSecond, 'Second');
-// Throws an error:
 // TypeError [ERR_AMBIGUOUS_ARGUMENT]
 
 // The string is only used (as message) in case the function does not throw:
 assert.throws(notThrowing, 'Second');
 // AssertionError [ERR_ASSERTION]: Missing expected exception: Second
 
 // If it was intended to match for the error message do this instead:
+// It does not throw because the error messages match.
 assert.throws(throwingSecond, /Second$/);
-// Does not throw because the error messages match.
+
+// If the error message does not match, the error from within the function is
+// not caught.
 assert.throws(throwingFirst, /Second$/);
-// Throws an error:
 // Error: First
 //     at throwingFirst (repl:2:9)
 ```