Declare test dependencies in [test] extra (#62)

Adding a test dependency on 'pytest' will cause colcon to use pytest
when running the package's tests, which yields a better experience than
the existing fallback to unittest.

.github/workflows/test.yml

@@ -29,13 +29,13 @@ jobs:
     - uses: actions/cache@v2
       with:
         path: ~/.cache/pip
-        key: ${{ runner.os }}-pip-${{ hashFiles('**/requirements.txt') }}
+        key: ${{ runner.os }}-pip-${{ hashFiles('**/setup.cfg') }}
         restore-keys: |
           ${{ runner.os }}-pip-
 
     - name: Install pip dependencies
       run: |
-       python -m pip install --upgrade --upgrade-strategy eager -r requirements.txt
+       python -m pip install --upgrade --upgrade-strategy eager .[test]
        python -m pip freeze
 
     - name: Run tests

setup.cfg

@@ -36,10 +36,20 @@ install_requires =
     sphinx-rtd-theme
     myst-parser
 packages = find:
-tests_require =
+zip_safe = false
+
+[options.extras_require]
+test =
     flake8
+    flake8-blind-except
+    flake8-builtins
+    flake8-class-newline
+    flake8-comprehensions
+    flake8-deprecated
+    flake8-docstrings
     flake8-import-order
-zip_safe = false
+    flake8-quotes
+    pytest
 
 # [options.packages.find]
 # exclude =