chore(generator): enable system tests

Author: ohmayr

packages/gapic-generator/noxfile.py

@@ -54,6 +54,7 @@
 )
 
 NEWEST_PYTHON = ALL_PYTHON[-2]
+SYSTEM_TEST_PYTHON_VERSIONS = ALL_PYTHON
 
 
 @nox.session(python=ALL_PYTHON)
@@ -816,12 +817,13 @@ def format(session):
     )
 
 
-@nox.session(python=ALL_PYTHON)
+@nox.session(python=SYSTEM_TEST_PYTHON_VERSIONS)
 def system(session):
-    # TODO(https://github.com/googleapis/google-cloud-python/issues/16190):
-    # Implement system test session.
-    """Run the system test suite (skipped for migration)."""
-    session.skip(f"system session is not yet implemented for gapic-generator-python.")
+    """Run the system test suite against Showcase."""
+    # Check the value of `RUN_SYSTEM_TESTS` env var. It defaults to true.
+    if os.environ.get("RUN_SYSTEM_TESTS", "true") == "false":
+        session.skip("RUN_SYSTEM_TESTS is set to false, skipping")
+    showcase(session)
 
 
 @nox.session(python=NEWEST_PYTHON)