Optional Mocha tests: if not pass mark as pending

mocha.optional.js

/**
 * Sometimes there is the need to have optional tests that may need to run conditionally as discussed in:
 * http://stackoverflow.com/questions/19075792/unit-tests-for-optional-units
 * This solution is good but if our tests are part of a test suite that runs against many different kinds of implementations 
 * it may be desirable to have optional tests that "pass" if they are supported and become "pending" if they fail.
 * This way we don't have to break the whole test suit because of an optional test breaksing and, if it passes, we'll know about it.
 */

function runOptionalTest(testName, failedMessage, testFn){
  if(!testFn){
    testFn = failedMessage;
    failedMessage = 'WARN: ' + testName + ' is not supported';
  }
  
  testFn(function(result){
    if(result){
      it(failedMessage);
    }
    else {
      it(testName, function(){});
    }
  });
}

describe('optional tests', function(){
  
  var successTest = function(done){
    done();
  };
  runOptionalTest('should do xyz', successTest);
  
  var failedTest = function(done){
    done(new Error('oops'));
  };
  runOptionalTest('should do xyz eventually', failedTest);    

});

// Result:
//  optional tests
//    ✓ should do xyz 
//    - WARN: should do xyz eventually is not supported

I've consolidated this on https://github.com/dmarcelino/it-optional.