Improving project structure with Hyper Python.

Signed-off-by: Cliff Hill <xlorep@darkhelm.org>

tests/__init__.py

@@ -0,0 +1 @@
+"""Test suite for the playlist package."""

tests/test_main.py

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+"""Test cases for the __main__ module."""
+import pytest
+from click.testing import CliRunner
+
+from playlist import __main__
+
+
+@pytest.fixture
+def runner() -> CliRunner:
+    """Fixture for invoking command-line interfaces."""
+    return CliRunner()
+
+
+def test_main_succeeds(runner: CliRunner) -> None:
+    """It exits with a status code of zero."""
+    result = runner.invoke(__main__.main)
+    assert result.exit_code == 0