Handle should.throw() assertion with no argument properly

third_party/WebKit/LayoutTests/webaudio/resources/audit.js

Index: third_party/WebKit/LayoutTests/webaudio/resources/audit.js
diff --git a/third_party/WebKit/LayoutTests/webaudio/resources/audit.js b/third_party/WebKit/LayoutTests/webaudio/resources/audit.js
index 7d337e6f087c41ed0cc55c907a9c55bf30119376..5177c596049b0cb0cc3f97eed71d125696aeeb8c 100644
--- a/third_party/WebKit/LayoutTests/webaudio/resources/audit.js
+++ b/third_party/WebKit/LayoutTests/webaudio/resources/audit.js
@@ -270,12 +270,16 @@ window.Audit = (function () {
         // Catch did not happen, so the test is failed.
         failDetail = '${actual} did not throw an exception.';
       } catch (error) {
-        if (this._expected === undefined) {
+        if (this._expected === null) {

[Raymond Toy, 2016/12/22 17:55:00]

What if someone did 

should(...).throw(undefined)

And is that what you want?

[hongchan, 2016/12/22 18:10:31]

Giving |undefined| as an argument will do nothing. The expected value will still
be |null|. The |null| value of the expected means that user did not provide
anything to expect. We can certainly introduce enums to clarify this, but I
don't think it's necessary.

+          // The expected error type was not given.
           didThrowCorrectly = true;
-          passDetail = '${actual} threw an exception of ' + error.name + '.';
+          passDetail = '${actual} threw an exception of ' + error.name + ': "'
+              + error.message + '".';

[Raymond Toy, 2016/12/22 17:55:00]

Nit: Can we actually throw anything other than an exception?  If not, then maybe
we can just remove "an exception of"?

[hongchan, 2016/12/22 18:10:31]

Good call. Done.

         } else if (error.name === this._expected) {
+          // The expected error type match the actual one.
           didThrowCorrectly = true;
-          passDetail = '${actual} threw ${expected} : "' + error.message + '".';
+          passDetail = '${actual} threw ${expected} as expected: "'
+              + error.message + '".';

[Raymond Toy, 2016/12/22 17:55:00]

Nit:  Similarly, can we just say "threw expected ${expected}", just to be
slightly more concise?

[hongchan, 2016/12/22 18:10:31]

Sure. Done.

         } else {
           didThrowCorrectly = false;
           failDetail = '${actual} threw "' + error.name