assert: respect assert.doesNotThrow message.

Special handling to detect when user has supplied a custom message.
Added a test for user message.
When testing if `actual` value is an error use
`util.isError` instead of `instanceof`.

Fixes: https://github.com/nodejs/node/issues/2385
PR-URL: https://github.com/nodejs/node/pull/2407
Reviewed-By: James M Snell <jasnell@gmail.com>

1 files changed, 8 insertions, 1 deletions

diff --git a/lib/assert.js b/lib/assert.js
index b4de551e280..7fc9e0c3426 100644
--- a/lib/assert.js
+++ b/lib/assert.js
@@ -330,7 +330,14 @@ function _throws(shouldThrow, block, expected, message) {
     fail(actual, expected, 'Missing expected exception' + message);
   }
 
-  if (!shouldThrow && expectedException(actual, expected)) {
+  const userProvidedMessage = typeof message === 'string';
+  const isUnwantedException = !shouldThrow && util.isError(actual);
+  const isUnexpectedException = !shouldThrow && actual && !expected;
+
+  if ((isUnwantedException &&
+      userProvidedMessage &&
+      expectedException(actual, expected)) ||
+      isUnexpectedException) {
     fail(actual, expected, 'Got unwanted exception' + message);
   }