lib: handle throw undefined in assert.throws()

And make `assert.doesNotThrow()` handle it as well.

Backport-PR-URL: #19230
PR-URL: #18029
Fixes: #18027
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Khaidi Chu <i@2333.moe>
Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/assert.js

@@ -31,6 +31,8 @@ const { inspect } = require('util');
 
 const assert = module.exports = ok;
 
+const NO_EXCEPTION_SENTINEL = {};
+
 // All of the following functions must throw an AssertionError
 // when a corresponding condition is not met, with a message that
 // may be undefined if not provided. All assertion methods provide
@@ -256,6 +258,7 @@ function getActual(block) {
   } catch (e) {
     return e;
   }
+  return NO_EXCEPTION_SENTINEL;
 }
 
 // Expected to throw an error.
@@ -273,7 +276,7 @@ assert.throws = function throws(block, error, message) {
     error = null;
   }
 
-  if (actual === undefined) {
+  if (actual === NO_EXCEPTION_SENTINEL) {
     let details = '';
     if (error && error.name) {
       details += ` (${error.name})`;
@@ -294,7 +297,7 @@ assert.throws = function throws(block, error, message) {
 
 assert.doesNotThrow = function doesNotThrow(block, error, message) {
   const actual = getActual(block);
-  if (actual === undefined)
+  if (actual === NO_EXCEPTION_SENTINEL)
     return;
 
   if (typeof error === 'string') {
@@ -308,7 +311,7 @@ assert.doesNotThrow = function doesNotThrow(block, error, message) {
       actual,
       expected: error,
       operator: 'doesNotThrow',
-      message: `Got unwanted exception${details}\n${actual.message}`,
+      message: `Got unwanted exception${details}\n${actual && actual.message}`,
       stackStartFn: doesNotThrow
     });
   }

test/parallel/test-assert.js

@@ -857,4 +857,16 @@ common.expectsError(
       message: "message: expected '', not 'foo'"
     }
   );
+
+  // eslint-disable-next-line no-throw-literal
+  assert.throws(() => { throw undefined; }, /undefined/);
+  common.expectsError(
+    // eslint-disable-next-line no-throw-literal
+    () => assert.doesNotThrow(() => { throw undefined; }),
+    {
+      type: assert.AssertionError,
+      code: 'ERR_ASSERTION',
+      message: 'Got unwanted exception.\nundefined'
+    }
+  );
 }