Add a limited but functional test

setup.cfg

@@ -24,3 +24,4 @@ dev =
     isort>=4.3.21
     pre-commit
     pudb
+    pytest

tests/test_oxo.py

@@ -1,5 +1,12 @@
+from typer.testing import CliRunner
+
 from oxo import __version__
+from oxo.cli import app
+
+runner = CliRunner()
 
 
 def test_version():
-    assert __version__ == "0.1.0"
+    result = runner.invoke(app, ["--version"])
+    assert result.exit_code == 0
+    assert __version__ == result.stdout.strip()