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assert: improve error messages
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From now on all error messages produced by `assert` in strict mode
will produce a error diff.

Backport-PR-URL: #19230
PR-URL: #17615
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Matteo Collina <[email protected]>
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@BridgeAR @MylesBorins
BridgeAR authored and MylesBorins committed Mar 20, 2018
1 parent c18ac52 commit 5aa3a2d
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Showing 4 changed files with 332 additions and 10 deletions.
33 changes: 33 additions & 0 deletions doc/api/assert.md
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Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,9 @@ For more information about the used equality comparisons see
<!-- YAML
added: REPLACEME
changes:
- version: REPLACEME
pr-url: https://github.com/nodejs/node/pull/REPLACEME
description: Added error diffs to the strict mode
- version: REPLACEME
pr-url: https://github.com/nodejs/node/pull/17002
description: Added strict mode to the assert module.
Expand All @@ -26,12 +29,42 @@ When using the `strict mode`, any `assert` function will use the equality used i
the strict function mode. So [`assert.deepEqual()`][] will, for example, work the
same as [`assert.deepStrictEqual()`][].

On top of that, error messages which involve objects produce an error diff
instead of displaying both objects. That is not the case for the legacy mode.

It can be accessed using:

```js
const assert = require('assert').strict;
```

Example error diff (the `expected`, `actual`, and `Lines skipped` will be on a
single row):

```js
const assert = require('assert').strict;

assert.deepEqual([[[1, 2, 3]], 4, 5], [[[1, 2, '3']], 4, 5]);
```

```diff
AssertionError [ERR_ASSERTION]: Input A expected to deepStrictEqual input B:
+ expected
- actual
... Lines skipped

[
[
...
2,
- 3
+ '3'
],
...
5
]
```

## Legacy mode

> Stability: 0 - Deprecated: Use strict mode instead.
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16 changes: 12 additions & 4 deletions lib/assert.js
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Original file line number Diff line number Diff line change
Expand Up @@ -25,6 +25,10 @@ const { isDeepEqual, isDeepStrictEqual } =
const errors = require('internal/errors');
const { inspect } = require('util');

const ERR_DIFF_DEACTIVATED = 0;
const ERR_DIFF_NOT_EQUAL = 1;
const ERR_DIFF_EQUAL = 2;

// The assert module provides functions that throw
// AssertionError's when particular conditions are not met. The
// assert module must conform to the following interface.
Expand Down Expand Up @@ -154,7 +158,8 @@ assert.deepStrictEqual = function deepStrictEqual(actual, expected, message) {
expected,
message,
operator: 'deepStrictEqual',
stackStartFn: deepStrictEqual
stackStartFn: deepStrictEqual,
errorDiff: this === strict ? ERR_DIFF_EQUAL : ERR_DIFF_DEACTIVATED
});
}
};
Expand All @@ -167,7 +172,8 @@ function notDeepStrictEqual(actual, expected, message) {
expected,
message,
operator: 'notDeepStrictEqual',
stackStartFn: notDeepStrictEqual
stackStartFn: notDeepStrictEqual,
errorDiff: this === strict ? ERR_DIFF_NOT_EQUAL : ERR_DIFF_DEACTIVATED
});
}
}
Expand All @@ -180,7 +186,8 @@ assert.strictEqual = function strictEqual(actual, expected, message) {
expected,
message,
operator: '===',
stackStartFn: strictEqual
stackStartFn: strictEqual,
errorDiff: this === strict ? ERR_DIFF_EQUAL : ERR_DIFF_DEACTIVATED
});
}
};
Expand All @@ -194,7 +201,8 @@ assert.notStrictEqual = function notStrictEqual(actual, expected, message) {
expected,
message,
operator: '!==',
stackStartFn: notStrictEqual
stackStartFn: notStrictEqual,
errorDiff: this === strict ? ERR_DIFF_NOT_EQUAL : ERR_DIFF_DEACTIVATED
});
}
};
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150 changes: 146 additions & 4 deletions lib/internal/errors.js
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Original file line number Diff line number Diff line change
Expand Up @@ -78,22 +78,164 @@ function makeNodeError(Base) {
};
}

function createErrDiff(actual, expected, operator) {
var other = '';
var res = '';
var lastPos = 0;
var end = '';
var skipped = false;
const util = lazyUtil();
const actualLines = util
.inspect(actual, { compact: false }).split('\n');
const expectedLines = util
.inspect(expected, { compact: false }).split('\n');
const msg = `Input A expected to ${operator} input B:\n` +
'\u001b[32m+ expected\u001b[39m \u001b[31m- actual\u001b[39m';
const skippedMsg = ' ... Lines skipped';

// Remove all ending lines that match (this optimizes the output for
// readability by reducing the number of total changed lines).
var a = actualLines[actualLines.length - 1];
var b = expectedLines[expectedLines.length - 1];
var i = 0;
while (a === b) {
if (i++ < 2) {
end = `\n ${a}${end}`;
} else {
other = a;
}
actualLines.pop();
expectedLines.pop();
a = actualLines[actualLines.length - 1];
b = expectedLines[expectedLines.length - 1];
}
if (i > 3) {
end = `\n...${end}`;
skipped = true;
}
if (other !== '') {
end = `\n ${other}${end}`;
other = '';
}

const maxLines = Math.max(actualLines.length, expectedLines.length);
var printedLines = 0;
for (i = 0; i < maxLines; i++) {
// Only extra expected lines exist
const cur = i - lastPos;
if (actualLines.length < i + 1) {
if (cur > 1 && i > 2) {
if (cur > 4) {
res += '\n...';
skipped = true;
} else if (cur > 3) {
res += `\n ${expectedLines[i - 2]}`;
printedLines++;
}
res += `\n ${expectedLines[i - 1]}`;
printedLines++;
}
lastPos = i;
other += `\n\u001b[32m+\u001b[39m ${expectedLines[i]}`;
printedLines++;
// Only extra actual lines exist
} else if (expectedLines.length < i + 1) {
if (cur > 1 && i > 2) {
if (cur > 4) {
res += '\n...';
skipped = true;
} else if (cur > 3) {
res += `\n ${actualLines[i - 2]}`;
printedLines++;
}
res += `\n ${actualLines[i - 1]}`;
printedLines++;
}
lastPos = i;
res += `\n\u001b[31m-\u001b[39m ${actualLines[i]}`;
printedLines++;
// Lines diverge
} else if (actualLines[i] !== expectedLines[i]) {
if (cur > 1 && i > 2) {
if (cur > 4) {
res += '\n...';
skipped = true;
} else if (cur > 3) {
res += `\n ${actualLines[i - 2]}`;
printedLines++;
}
res += `\n ${actualLines[i - 1]}`;
printedLines++;
}
lastPos = i;
res += `\n\u001b[31m-\u001b[39m ${actualLines[i]}`;
other += `\n\u001b[32m+\u001b[39m ${expectedLines[i]}`;
printedLines += 2;
// Lines are identical
} else {
res += other;
other = '';
if (cur === 1 || i === 0) {
res += `\n ${actualLines[i]}`;
printedLines++;
}
}
// Inspected object to big (Show ~20 rows max)
if (printedLines > 20 && i < maxLines - 2) {
return `${msg}${skippedMsg}\n${res}\n...${other}\n...`;
}
}
return `${msg}${skipped ? skippedMsg : ''}\n${res}${other}${end}`;
}

class AssertionError extends Error {
constructor(options) {
if (typeof options !== 'object' || options === null) {
throw new exports.TypeError('ERR_INVALID_ARG_TYPE', 'options', 'Object');
}
var { actual, expected, message, operator, stackStartFn } = options;
if (message) {
var {
actual,
expected,
message,
operator,
stackStartFn,
errorDiff = 0
} = options;

if (message != null) {
super(message);
} else {
const util = lazyUtil();
if (actual && actual.stack && actual instanceof Error)
actual = `${actual.name}: ${actual.message}`;
if (expected && expected.stack && expected instanceof Error)
expected = `${expected.name}: ${expected.message}`;
super(`${util.inspect(actual).slice(0, 128)} ` +
`${operator} ${util.inspect(expected).slice(0, 128)}`);

if (errorDiff === 0) {
let res = util.inspect(actual);
let other = util.inspect(expected);
if (res.length > 128)
res = `${res.slice(0, 125)}...`;
if (other.length > 128)
other = `${other.slice(0, 125)}...`;
super(`${res} ${operator} ${other}`);
} else if (errorDiff === 1) {
// In case the objects are equal but the operator requires unequal, show
// the first object and say A equals B
const res = util
.inspect(actual, { compact: false }).split('\n');

if (res.length > 20) {
res[19] = '...';
while (res.length > 20) {
res.pop();
}
}
// Only print a single object.
super(`Identical input passed to ${operator}:\n${res.join('\n')}`);
} else {
super(createErrDiff(actual, expected, operator));
}
}

this.generatedMessage = !message;
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