title: Detect unwanted functions (fdescribe, describe.only) as Gulp task
body: <p>How can the usage of unwanted functions in code base be detected in Node, particularly Gulp?</p>
  
  <p>I'm after checking for unintentionally spoiled specs, i.e <code>ddescribe</code>/<code>fdescribe</code> and <code>iit</code>/<code>fit</code> for Jasmine or <code>.only</code> and <code>.skip</code> for Mocha:</p>
  
  <pre><code>// should be reported
  fdescribe(function () {
    // should not be reported
    it(function () {
      var fit = ...;
      this.fit = ...;
    });
  
    // should not be reported
    // fit(function () { ... });
  
    //  should be reported
    xit(function () { ... });
  
    //  should be reported
    fit(function () { ... });
  });
  </code></pre>
  
  <hr>
  
  <pre><code>// should be reported
  describe.only(function () {
    // should not be reported
    it(function () { ... });
  
    // should not be reported
    // it.only(function () { ... });
  
    //  should be reported
    it.skip(function () { ... });
  
    //  should be reported
    it.only(function () { ... });
  });
  </code></pre>
  
  <p>The task should exit with error and output file names and line numbers where listed functions are used. </p>
  
  <p>The commented ones surely don't have to be detected, as well as functions/properties with the same name (most likely <code>fit</code>), so simple regexp match is not an option here (like it would be for <code>console.*</code>). Some AST-based solution that accepts user-defined function names would be appreciated.</p>