fix typo

Co-authored-by: Peter Kalverla <[email protected]>

Author: SarahAlidoost

_episodes/08-development-setup.md

@@ -298,7 +298,7 @@ To explore other tools, have a look at ESMValTool documentation on
 ### Run unit tests
 
 Previous section introduced some tools to check code style and quality.
-What it hasen’t done is show us how to tell whether our code is getting the right answer.
+What it hasn’t done is show us how to tell whether our code is getting the right answer.
 To achieve that, we need to write and run tests for widely-used functions.
 ESMValTool comes with a lot of tests that are in the folder ``tests``.