assert: fix misformatted error message

Before: `Missing expected exception..`

Afer: `Missing expected exception.`

PR-URL: https://github.com/nodejs/node/pull/11254
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>

lib/assert.js

@@ -341,8 +341,8 @@ function _throws(shouldThrow, block, expected, message) {
 
   actual = _tryBlock(block);
 
-  message = (expected && expected.name ? ' (' + expected.name + ').' : '.') +
-            (message ? ' ' + message : '.');
+  message = (expected && expected.name ? ' (' + expected.name + ')' : '') +
+            (message ? ': ' + message : '.');
 
   if (shouldThrow && !actual) {
     fail(actual, expected, 'Missing expected exception' + message);

test/parallel/test-assert.js

@@ -490,6 +490,29 @@ a.throws(makeBlock(a.deepEqual, args, []));
   a.doesNotThrow(makeBlock(a.deepEqual, someArgs, sameArgs));
 }
 
+// check messages from assert.throws()
+{
+  assert.throws(
+    () => { a.throws(() => {}); },
+    /^AssertionError: Missing expected exception\.$/
+  );
+
+  assert.throws(
+    () => { a.throws(() => {}, TypeError); },
+    /^AssertionError: Missing expected exception \(TypeError\)\.$/
+  );
+
+  assert.throws(
+    () => { a.throws(() => {}, 'fhqwhgads'); },
+    /^AssertionError: Missing expected exception: fhqwhgads$/
+  );
+
+  assert.throws(
+    () => { a.throws(() => {}, TypeError, 'fhqwhgads'); },
+    /^AssertionError: Missing expected exception \(TypeError\): fhqwhgads$/
+  );
+}
+
 const circular = {y: 1};
 circular.x = circular;
 
@@ -535,7 +558,7 @@ testAssertionMessage({a: NaN, b: Infinity, c: -Infinity},
     });
   } catch (e) {
     threw = true;
-    assert.strictEqual(e.message, 'Missing expected exception..');
+    assert.strictEqual(e.message, 'Missing expected exception.');
   }
   assert.ok(threw);
 }