Improve assertion messages in uncaught exceptions

Wrap all assert.* methods in a try/catch that appends the
current test to the Error object and rethrows.

This allows us to get the corresponding Test object in the
`uncaughtException` event.

Before:

   uncaught undefined: AssertionError: 'blah' === 'blahs'
    at Blah.<anonymous> (/home/user/test.js:15:17)
    ...

After:

   test.js testing blah(): AssertionError: 'blah' === 'blahs'
    at Blah.<anonymous> (/home/user/test.js:15:17)
    ...

bin/expresso

@@ -549,6 +549,24 @@ assert.response = function(server, req, res, msg) {
       }
 };
 
+/**
+ * Custom assert module that tacks on the current test to every error
+ */
+var customAssert = { __proto__: assert };
+Object.keys(assert).forEach(function (method) {
+   customAssert[method] = function () {
+      try {
+         return assert[method].apply(assert, arguments);
+      } catch (err) {
+         // 'this' is this assert object from the test
+         if (this._test) {
+            err._test = this._test;
+         }
+         throw err;
+      }
+   };
+});
+
 /**
  * Pad the given string to the maximum width provided.
  *
@@ -885,7 +903,7 @@ function Test(options) {
     this._failed = [];
     this._pending = [];
     this._beforeExit = [];
-    this.assert = { __proto__: assert, _test: this };
+    this.assert = { __proto__: customAssert, _test: this };
 
     var test = this;
     process.on('beforeExit', function() {
@@ -976,11 +994,10 @@ Test.prototype.runParallel = function() {
 Test.prototype.error = function(err) {
     if (!err._reported) {
         ++failures;
+        var test = err._test || this;
         var name = err.name,
             stack = err.stack ? err.stack.replace(err.name, '') : '',
-            label = this.title === 'uncaught'
-                ? this.title
-                : this.suite + ' ' + this.title;
+            label = test.suite + ' ' + test.title;
         print('\n   [bold]{' + label + '}: [red]{' + name + '}' + stack + '\n');
         err._reported = true;
     }

test/local-assert.test.js

@@ -5,6 +5,14 @@ exports['first'] = function(beforeExit, assert) {
     process.nextTick(function() {
         assert.equal(assert._test.suite, 'local-assert.test.js');
         assert.equal(assert._test.title, 'first');
+        try {
+           var error = false;
+           assert.ok(false);
+        } catch (err) {
+           assert.equal(err._test, assert._test);
+           error = true;
+        }
+        assert.ok(error);
     });
 };