Add deprecation warning for the mol command (#3407)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Sorin Sbarnea <[email protected]>

setup.cfg

@@ -117,7 +117,7 @@ lint =
 [options.entry_points]
 console_scripts =
     molecule = molecule.__main__:main
-    mol = molecule.__main__:main
+    mol = molecule.__main__:mol_deprecation_notice
 molecule.driver =
     delegated = molecule.driver.delegated:Delegated
 molecule.verifier =

src/molecule/__main__.py

@@ -19,7 +19,22 @@
 #  DEALINGS IN THE SOFTWARE.
 """Molecule CLI main entry point."""
 
+import warnings
+
 from molecule.shell import main
 
+
+def mol_deprecation_notice():
+    """Display a deprecation notice about mol command."""
+    try:
+        main()
+    except BaseException:
+        warnings.warn(
+            "The `mol` command is deprecated and will be removed in a future version of Molecule. If you wish to continue using it, please create an alias that calls `molecule`.",
+            category=UserWarning,
+        )
+        raise
+
+
 if __name__ == "__main__":
     main()

src/molecule/test/unit/test_api.py

@@ -49,5 +49,6 @@ def test_cli_mol():
     cmd_mol = ["mol", "--version"]
     y = util.run_command(cmd_mol)
     assert x.returncode == y.returncode
-    assert x.stderr == y.stderr
-    assert x.stdout == y.stdout
+    assert x.stderr in y.stderr
+    assert x.stdout in y.stdout
+    assert "UserWarning" in y.stdout