title: How to test a conditional expression in mocha / sinon
body: <p>I have some function like this:</p>
  
  <pre><code>abc(prop) {
        const x = aComplexFunction(this.productData, 'productStatus');
        let result;
  
        /* istanbul-ignore-next */
        if (x) {
          const key = (x[prop]) ? 'enabled' : 'notEnabled';
  
          result = `wayOfLife.${key}`;
        }
  
        return result;
      },
  </code></pre>
  
  <p>My coverage says the 'enabled' part is not covered. How to fix this</p>