feat: promote 3.9 to main version (as it is in Cloudtops now for loca…

…l testing) and add a small unit test for persoanl use (#292)

noxfile.py

@@ -27,7 +27,7 @@
 
 
 # Python version used for linting.
-DEFAULT_PYTHON_VERSION = "3.7"
+DEFAULT_PYTHON_VERSION = "3.9"
 
 # Python versions used for testing.
 PYTHON_VERSIONS = ["3.7", "3.8", "3.9"]
@@ -64,6 +64,11 @@ def unit(session):
     )
 
 
+@nox.session(python=DEFAULT_PYTHON_VERSION, venv_backend="venv")
+def unit_small(session):
+    unit(session)
+
+
 @nox.session(python=PYTHON_VERSIONS, venv_backend="venv")
 def samples(session):
     """Run the snippets test suite."""