Mark slow test

Author: kfarnung

.github/workflows/2018.yml

@@ -45,4 +45,4 @@ jobs:
         if: ${{ !contains(matrix.python-version, '2.' )}}
 
       - name: Test with pytest
-        run: pytest
+        run: pytest -n auto --slow

2018/day21/test_day21.py

@@ -4,6 +4,8 @@
 https://adventofcode.com/2018/day/21
 """
 
+import pytest
+
 from os import path
 from .day21 import run_part1, run_part2
 
@@ -23,6 +25,7 @@ def test_part1():
         assert run_part1(file_content) == 6619857
 
 
+@pytest.mark.slow
 def test_part2():
     """Tests for Part 2."""
     with open(_INPUT_FILE, 'r') as input_file:

2018/requirements.txt

@@ -1,3 +1,4 @@
 pylint
 pytest
+pytest-skip-slow
 pytest-xdist