Run tests in parallel on multi-core systems

Uses pytest-xdist to run tests on two cores simultaneously, speeding up
test runs by nearly 40%.

pyproject.toml

@@ -51,6 +51,7 @@ pytest = "~5.3.5"
 pytest-cov = "^2.8"
 pytest-pythonpath = "^0.7.3"
 pytest-sugar = "^0.9.2"
+pytest-xdist = "^1.31"
 tox = "^3.13"
 flake8 = "^3.7"
 flake8-import-order = "^0.18.1"

requirements/test.pip

@@ -3,6 +3,7 @@ Pygments==2.6.1
 mock
 pytest==5.3.5
 pytest-cov
+pytest-xdist
 
 # Optional Packages
 Markdown >= 3.1

tox.ini

@@ -27,6 +27,7 @@ commands =
 filterwarnings =
     default::DeprecationWarning
     error:.*:Warning:pelican
+addopts = -n 2
 
 [flake8]
 application-import-names = pelican