allow test_docs to fail if any code block fails

test_docs.py

@@ -2,18 +2,24 @@
 import re
 import subprocess
 import logging
+import sys
 
 
 def run_python_code_block(code):
     return subprocess.check_output(['python3', '-s'], input=code.encode())
 
 
+exitcode = 0
+
 for path in Path('.').glob('**/*.md'):
     text = path.read_text()
     for code in re.findall('```python(.*?)```', text, re.S):
         try:
             print(f'running {path}')
             run_python_code_block(code)
         except Exception as exc:
+            exitcode = 1
             logging.exception(
                 f'code block failed in {path}\n\n```python{code}```\n\n')
+
+sys.exit(exitcode)