Add code coverage gathering

tests/test_cli.py

@@ -1,10 +1,15 @@
 import click.testing
+import pytest
 
 from habitmove import cli
 
 
-def test_cli_fails_without_file():
-    runner = click.testing.CliRunner()
+@pytest.fixture
+def runner():
+    return click.testing.CliRunner()
+
+
+def test_cli_fails_without_file(runner):
     result = runner.invoke(cli.main)
     assert result.exit_code == 2
     assert "Missing argument" in result.output