title: Jest code coverage with tests written in CoffeeScript
body: <p>Is there a way to run the Jest coverage tool over unit tests that are written in CoffeeScript? The coverage report always tells me 100% coverage.</p>
  
  <pre><code>jest --coverage
  
  ----------|----------|----------|----------|----------|----------------|
  File      |  % Stmts | % Branch |  % Funcs |  % Lines |Uncovered Lines |
  ----------|----------|----------|----------|----------|----------------|
  ----------|----------|----------|----------|----------|----------------|
  All files |      100 |      100 |      100 |      100 |                |
  ----------|----------|----------|----------|----------|----------------|
  </code></pre>
  
  <p>I am already transpiling CoffeeScript to JavaScript with following Jest preprocessor</p>
  
  <pre><code>var coffee = require('coffee-script');
  
  module.exports = {
    // CoffeeScript files can be .coffee or .litcoffee
    process: function(src, path) {
      if (coffee.helpers.isCoffee(path)) {
        return coffee.compile(src, {
          bare: true,
          literate: coffee.helpers.isLiterate(path)
        });
      }
      return src;
    }
  };
  </code></pre>