Add promise support (close #329, close #1036)

lib/runnable.js

@@ -170,12 +170,12 @@ Runnable.prototype.run = function(fn){
 
   // timeout
   if (this.async) {
-    if (ms) {
-      this.timer = setTimeout(function(){
+    this.timer = setTimeout(function(){
+      if (!finished) {
         done(new Error('timeout of ' + ms + 'ms exceeded'));
         self.timedOut = true;
-      }, ms);
-    }
+      }
+    }, ms);
   }
 
   // called multiple times
@@ -218,10 +218,22 @@ Runnable.prototype.run = function(fn){
 
   // sync
   try {
-    if (!this.pending) this.fn.call(ctx);
-    this.duration = new Date - start;
-    fn();
+    if (!this.pending) {
+      var result = this.fn.call(ctx);
+      if (result && typeof result.then === 'function') {
+        result.then(
+          function(){
+            done();
+          },
+          done
+        );
+      } else {
+        done();
+      }
+    } else {
+      done();
+    }
   } catch (err) {
-    fn(err);
+    done(err);
   }
 };