assert: improve assert.throws

This switches the assert.throws output to the one used in strict mode
if a error object is used for comparison. From now on it will show
the complete difference between two objects instead of only showing
the first failing property.

It also fixes detecting properties with a undefined value and fails
in case the thrown error does not contain the value at all.

PR-URL: https://github.com/nodejs/node/pull/19463
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/assert.js

@@ -366,13 +366,38 @@ assert.notStrictEqual = function notStrictEqual(actual, expected, message) {
   }
 };
 
-function compareExceptionKey(actual, expected, key, msg) {
+class Comparison {
-  if (!isDeepStrictEqual(actual[key], expected[key])) {
+  constructor(obj, keys) {
+    for (const key of keys) {
+      if (key in obj)
+        this[key] = obj[key];
+    }
+  }
+}
+
+function compareExceptionKey(actual, expected, key, message, keys) {
+  if (!(key in actual) || !isDeepStrictEqual(actual[key], expected[key])) {
+    if (!message) {
+      // Create placeholder objects to create a nice output.
+      const a = new Comparison(actual, keys);
+      const b = new Comparison(expected, keys);
+
+      const tmpLimit = Error.stackTraceLimit;
+      Error.stackTraceLimit = 0;
+      const err = new AssertionError({
+        actual: a,
+        expected: b,
+        operator: 'deepStrictEqual',
+        stackStartFn: assert.throws,
+        errorDiff: ERR_DIFF_EQUAL
+      });
+      Error.stackTraceLimit = tmpLimit;
+      message = err.message;
+    }
     innerFail({
-      actual: actual[key],
+      actual,
-      expected: expected[key],
+      expected,
-      message: msg || `${key}: expected ${inspect(expected[key])}, ` +
+      message,
-                      `not ${inspect(actual[key])}`,
       operator: 'throws',
       stackStartFn: assert.throws
     });
@@ -389,16 +414,14 @@ function expectedException(actual, expected, msg) {
         'expected', ['Function', 'RegExp'], expected
       );
     }
-    // The name and message could be non enumerable. Therefore test them
+    const keys = Object.keys(expected);
-    // explicitly.
+    // Special handle errors to make sure the name and the message are compared
-    if ('name' in expected) {
+    // as well.
-      compareExceptionKey(actual, expected, 'name', msg);
+    if (expected instanceof Error) {
+      keys.push('name', 'message');
     }
-    if ('message' in expected) {
+    for (const key of keys) {
-      compareExceptionKey(actual, expected, 'message', msg);
+      compareExceptionKey(actual, expected, key, msg, keys);
-    }
-    for (const key of Object.keys(expected)) {
-      compareExceptionKey(actual, expected, key, msg);
     }
     return true;
   }

test/message/assert_throws_stack.out

@@ -2,7 +2,13 @@ assert.js:*
   throw new AssertionError(obj);
   ^
 
-AssertionError [ERR_ASSERTION]: bar: expected true, not undefined
+AssertionError [ERR_ASSERTION]: Input A expected to deepStrictEqual input B:
++ expected - actual
+
+- Comparison {}
++ Comparison {
++   bar: true
++ }
     at Object.<anonymous> (*assert_throws_stack.js:*:*)
     at *
     at *

test/parallel/test-assert-fail-deprecation.js

@@ -38,11 +38,7 @@ assert.throws(() => {
   assert.fail(typeof 1, 'object', new TypeError('another custom message'));
 }, {
   name: 'TypeError',
-  message: 'another custom message',
+  message: 'another custom message'
-  operator: undefined,
-  actual: undefined,
-  expected: undefined,
-  code: undefined
 });
 
 // No third arg (but a fourth arg)

test/parallel/test-assert-fail.js

@@ -33,8 +33,5 @@ assert.throws(() => {
   assert.fail(new TypeError('custom message'));
 }, {
   name: 'TypeError',
-  message: 'custom message',
+  message: 'custom message'
-  operator: undefined,
-  actual: undefined,
-  expected: undefined
 });

test/parallel/test-assert.js

@@ -34,6 +34,12 @@ const { writeFileSync, unlinkSync } = require('fs');
 const { inspect } = require('util');
 const a = assert;
 
+const colors = process.stdout.isTTY && process.stdout.getColorDepth() > 1;
+const start = 'Input A expected to deepStrictEqual input B:';
+const actExp = colors ?
+  '\u001b[32m+ expected\u001b[39m \u001b[31m- actual\u001b[39m' :
+  '+ expected - actual';
+
 assert.ok(a.AssertionError.prototype instanceof Error,
           'a.AssertionError instanceof Error');
 
@@ -436,11 +442,6 @@ common.expectsError(
   Error.stackTraceLimit = tmpLimit;
 
   // Test error diffs.
-  const colors = process.stdout.isTTY && process.stdout.getColorDepth() > 1;
-  const start = 'Input A expected to deepStrictEqual input B:';
-  const actExp = colors ?
-    '\u001b[32m+ expected\u001b[39m \u001b[31m- actual\u001b[39m' :
-    '+ expected - actual';
   const plus = colors ? '\u001b[32m+\u001b[39m' : '+';
   const minus = colors ? '\u001b[31m-\u001b[39m' : '-';
   let message = [
@@ -765,24 +766,32 @@ common.expectsError(
   errObj.code = 404;
   assert.throws(errFn, errObj);
 
-  errObj.code = '404';
+  // Fail in case a expected property is undefined and not existent on the
-  common.expectsError(
+  // error.
+  errObj.foo = undefined;
+  assert.throws(
     () => assert.throws(errFn, errObj),
     {
       code: 'ERR_ASSERTION',
-      type: assert.AssertionError,
+      name: 'AssertionError [ERR_ASSERTION]',
-      message: 'code: expected \'404\', not 404'
+      message: `${start}\n${actExp}\n\n` +
+               "  Comparison {\n    name: 'TypeError',\n" +
+               "    message: 'Wrong value',\n-   code: 404\n" +
+               '+   code: 404,\n+   foo: undefined\n  }'
     }
   );
 
-  errObj.code = 404;
+  // Show multiple wrong properties at the same time.
-  errObj.foo = 'bar';
+  errObj.code = '404';
-  common.expectsError(
+  assert.throws(
     () => assert.throws(errFn, errObj),
     {
       code: 'ERR_ASSERTION',
-      type: assert.AssertionError,
+      name: 'AssertionError [ERR_ASSERTION]',
-      message: 'foo: expected \'bar\', not undefined'
+      message: `${start}\n${actExp}\n\n` +
+               "  Comparison {\n    name: 'TypeError',\n" +
+               "    message: 'Wrong value',\n-   code: 404\n" +
+               "+   code: '404',\n+   foo: undefined\n  }"
     }
   );
 
@@ -806,20 +815,24 @@ common.expectsError(
   );
 
   assert.throws(() => { throw new Error('e'); }, new Error('e'));
-  common.expectsError(
+  assert.throws(
     () => assert.throws(() => { throw new TypeError('e'); }, new Error('e')),
     {
-      type: assert.AssertionError,
+      name: 'AssertionError [ERR_ASSERTION]',
       code: 'ERR_ASSERTION',
-      message: "name: expected 'Error', not 'TypeError'"
+      message: `${start}\n${actExp}\n\n` +
+               "  Comparison {\n-   name: 'TypeError',\n+   name: 'Error'," +
+               "\n    message: 'e'\n  }"
     }
   );
-  common.expectsError(
+  assert.throws(
     () => assert.throws(() => { throw new Error('foo'); }, new Error('')),
     {
-      type: assert.AssertionError,
+      name: 'AssertionError [ERR_ASSERTION]',
       code: 'ERR_ASSERTION',
-      message: "message: expected '', not 'foo'"
+      message: `${start}\n${actExp}\n\n` +
+               "  Comparison {\n    name: 'Error',\n-   message: 'foo'" +
+               "\n+   message: ''\n  }"
     }
   );