Implement the support for only modifier.

- Hack the test count number if only modifier is shown.

lib/runner.js

@@ -32,6 +32,7 @@ function Runner(opts) {
 	this.tests = {
 		concurrent: [],
 		serial: [],
+		only: [],
 		before: [],
 		after: [],
 		beforeEach: [],
@@ -97,7 +98,9 @@ Runner.prototype.addSkippedTest = function (title, cb) {
 	this.tests.concurrent.push(test);
 };
 
-Runner.prototype.addOnlyTest = function () {
+Runner.prototype.addOnlyTest = function (title, cb) {
+	this.stats.testCount++;
+	this.tests.only.push(new Test(title, cb));
 };
 
 Runner.prototype._runTestWithHooks = function (test) {
@@ -206,16 +209,20 @@ Runner.prototype.run = function () {
 			}
 		})
 		.then(function () {
-			return self.serial(tests.serial);
+			return self.concurrent(tests.only);
+		})
+		.then(function () {
+			return tests.only.length ? [] : self.serial(tests.serial);
 		})
 		.then(function () {
-			return self.concurrent(tests.concurrent);
+			return tests.only.length ? [] : self.concurrent(tests.concurrent);
 		})
 		.then(function () {
 			return eachSeries(tests.after, self._runTest.bind(self));
 		})
 		.catch(noop)
 		.then(function () {
+			stats.testCount = tests.only.length ? tests.only.length : stats.testCount;
 			stats.passCount = stats.testCount - stats.failCount;
 		});
 };