Resolve notebook len duplicate method

notebook/tests/selenium/test_dualmode_execute.py

@@ -76,6 +76,6 @@ def test_dualmode_execute(notebook):
 
 
     #Notebook will now have 8 cells, the index of the last cell will be 7
-    assert notebook.get_cells_length() == 8 #Cells where added
+    assert len(notebook) == 8 #Cells where added
     notebook.focus_cell(7)
     validate_notebook_state(notebook, 'command', 7)

notebook/tests/selenium/utils.py

@@ -226,10 +226,6 @@ class Notebook:
         JS = 'return Jupyter.notebook.get_cells().map(function(c) {return c.mode;})'
         return self.browser.execute_script(JS)
 
-    def get_cells_length(self):
-        JS = 'return IPython.notebook.get_cells().length;'
-        return self.browser.execute_script(JS)
-
     def get_cell_type(self, index=0):
         JS = 'return Jupyter.notebook.get_cell({}).cell_type'.format(index)
         return self.browser.execute_script(JS)