Added protection against multiple calls to done(). Closes #35

great suggestion by guillermo

lib/runner.js

@@ -162,12 +162,19 @@ Runner.prototype.hook = function(name, fn){
  */
 
 Runner.prototype.runTest = function(fn){
-  var test = this.test;
+  var test = this.test
+    , self = this;
 
   // run the test
   try {
     // async
-    if (test.async) return test.run(fn);
+    if (test.async) return test.run(function(err){
+      if (test.finished) {
+        self.fail(test, new Error('done() called multiple times'));
+        return;
+      }
+      fn(err);
+    });
     // sync  
     process.nextTick(function(){
       test.run();

lib/test.js

@@ -73,6 +73,7 @@ Test.prototype.run = function(fn){
       clearTimeout(timer);
       self.duration = new Date - start;
       fn(err);
+      self.finished = true;
     });
   // sync
   } else {

test/unit/multiple.done.js

@@ -0,0 +1,10 @@
+
+describe('multiple calls to done()', function(){
+  it('should fail in a test-case', function(done){
+    process.nextTick(function(){
+      done();
+      // uncomment
+      // done();
+    });
+  })
+})