title: (Chai) assert.isBoolean is not a function - what i does wrong?
body: <p>There are little part of code:</p>
  
  <pre><code>driver.wait(function(){ 
      return driver.isElementPresent(webdriver.By.className(errElement));
  }, 3000, 'Element' + errElement + ' is not found').then(function(binaryVariable){
      assert.isTrue(binaryVariable, 'is not True');
        /*console.log(binaryVariable);
          console.log(typeof(binaryVariable));*/
  }); 
  </code></pre>
  
  <p>if I enable debug print, in the console appears </p>
  
  <pre><code>true
  boolean
  </code></pre>
  
  <p>It means that <code>driver.wait</code> returns boolean, so I try to check it via <code>assert.isTrue</code>. But I recieve error message <code>assert.isTrue is not a function</code>. What I does wrong?</p>