assert: wrap original error in ifError

It is hard to know where ifError is actually triggered due to the
original error being thrown.
This changes it by wrapping the original error in a AssertionError.
This has the positive effect of also making clear that it is indeed
a assertion function that triggered that error.

The original stack can still be accessed by checking the `actual`
property.

PR-URL: https://github.com/nodejs/node/pull/18247
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/parallel/test-assert-if-error.js

@@ -0,0 +1,82 @@
+'use strict';
+
+require('../common');
+const assert = require('assert').strict;
+/* eslint-disable no-restricted-properties */
+
+// Test that assert.ifError has the correct stack trace of both stacks.
+
+let err;
+// Create some random error frames.
+(function a() {
+  (function b() {
+    (function c() {
+      err = new Error('test error');
+    })();
+  })();
+})();
+
+const msg = err.message;
+const stack = err.stack;
+
+(function x() {
+  (function y() {
+    (function z() {
+      let threw = false;
+      try {
+        assert.ifError(err);
+      } catch (e) {
+        assert.equal(e.message, 'ifError got unwanted exception: test error');
+        assert.equal(err.message, msg);
+        assert.equal(e.actual, err);
+        assert.equal(e.actual.stack, stack);
+        assert.equal(e.expected, null);
+        assert.equal(e.operator, 'ifError');
+        threw = true;
+      }
+      assert(threw);
+    })();
+  })();
+})();
+
+assert.throws(
+  () => assert.ifError(new TypeError()),
+  {
+    message: 'ifError got unwanted exception: TypeError'
+  }
+);
+
+assert.throws(
+  () => assert.ifError({ stack: false }),
+  {
+    message: 'ifError got unwanted exception: { stack: false }'
+  }
+);
+
+assert.throws(
+  () => assert.ifError({ constructor: null, message: '' }),
+  {
+    message: 'ifError got unwanted exception: '
+  }
+);
+
+assert.doesNotThrow(() => { assert.ifError(null); });
+assert.doesNotThrow(() => { assert.ifError(); });
+assert.doesNotThrow(() => { assert.ifError(undefined); });
+assert.doesNotThrow(() => { assert.ifError(false); });
+
+// https://github.com/nodejs/node-v0.x-archive/issues/2893
+{
+  let threw = false;
+  try {
+    // eslint-disable-next-line no-restricted-syntax
+    assert.throws(() => {
+      assert.ifError(null);
+    });
+  } catch (e) {
+    threw = true;
+    assert.strictEqual(e.message, 'Missing expected exception.');
+    assert(!e.stack.includes('throws'), e.stack);
+  }
+  assert(threw);
+}