Count CPU cores via psutil for parallel testing

psutil does a much better job at accurately counting CPU cores,
of which pytest-xdist takes advantage for the purposes of running
tests concurrently.

pyproject.toml

@@ -49,6 +49,7 @@ typogrify = "^2.0"
 sphinx = "^3.0"
 sphinx_rtd_theme = "^0.5"
 livereload = "^2.6"
+psutil = {version = "^5.7", optional = true}
 pytest = "^6.0"
 pytest-cov = "^2.8"
 pytest-pythonpath = "^0.7.3"

requirements/test.pip

@@ -2,7 +2,7 @@
 Pygments==2.6.1
 pytest
 pytest-cov
-pytest-xdist
+pytest-xdist[psutil]
 
 # Optional Packages
 Markdown >= 3.1

tasks.py

@@ -14,7 +14,7 @@ VENV_PATH = Path(ACTIVE_VENV) if ACTIVE_VENV else (VENV_HOME / PKG_NAME)
 VENV = str(VENV_PATH.expanduser())
 VENV_BIN = Path(VENV) / Path(BIN_DIR)
 
-TOOLS = ["poetry", "pre-commit"]
+TOOLS = ["poetry", "pre-commit", "psutil"]
 POETRY = which("poetry") if which("poetry") else (VENV_BIN / "poetry")
 PRECOMMIT = (
     which("pre-commit") if which("pre-commit") else (VENV_BIN / "pre-commit")