Add testing duration improvements (#440)

* Install pytest xdist plugin

* Run tests with pytest-xdist

* Use mypy cache in tox

This makes running mypy from tox much
faster (e.g., with `tox -e typing`).

* Store and load mypy cache in GH workflow

* Use `black` cache in tox

* Add `pytest-cov` plugin

In order to get coverage when using the
`pytest-xdist` plugin we should use
`pytest-cov`.

* Move `pytest-xdist` to dev-packages in Pipfile

---------

Co-authored-by: Martin Vrachev <[email protected]>

.coveragerc

@@ -0,0 +1,2 @@
+[run]
+omit = tests/*

.github/workflows/ci.yml

@@ -29,8 +29,25 @@ jobs:
     - name: Test Build binary wheel and source tarball
       run: python3 -m build --sdist --wheel --outdir dist/ .
 
+    - name: Restore mypy cache
+      id: cache-mypy-restore
+      uses: actions/cache/restore@v3
+      with:
+        path: |
+          .mypy_cache
+        key: ${{ runner.os }}-py${{ matrix.python-versions }}-mypy-${{ hashFiles('**/.mypy_cache') }}
+
     - name: Run Python tests
-      run: make tests
+      run: |
+        make tests
+
+    - name: Save mypy cache
+      id: cache-mypy-save
+      uses: actions/cache/save@v3
+      with:
+        path: |
+          .mypy_cache
+        key: ${{ runner.os }}-py${{ matrix.python-versions }}-mypy-${{ hashFiles('**/.mypy_cache') }}
 
     - name: Codecov
       uses: codecov/codecov-action@eaaf4bedf32dbdc6b720b63067d99c4d77d6047d

Pipfile

@@ -23,6 +23,8 @@ isort = "*"
 flake8 = "*"
 tox = "*"
 pytest = "*"
+pytest-cov = "*"
+pytest-xdist = "*"
 coverage = "*"
 mypy = "*"
 pip = "*"