BUG: notebooks are one-based indexed, so we should not zero-index

Author: bsipocz

nbval/plugin.py

@@ -311,7 +311,7 @@ def collect(self):
         self.nb = nbformat.read(str(self.fspath), as_version=4)
 
         # Start the cell count
-        cell_num = 0
+        cell_num = 1
 
         # Iterate over the cells in the notebook
         for cell in self.nb.cells: