[test] Add code coverage framework

Implement a comprehensive test coverage framework that integrates with pytest-cov
to generate code coverage reports for the yt-dlp codebase. Key components:

- Configuration file (.coveragerc) with appropriate include/exclude patterns
- Helper script (run_coverage.py) with parallel report generation
- GitHub Actions workflow for automatic coverage reporting on PRs and pushes
- Support for Hatch testing environment and CLI integration
- Testing documentation for running coverage reports
- Sample test for demonstrating coverage reporting

test/README.md

@@ -0,0 +1,39 @@
+# yt-dlp Tests
+
+This directory contains tests for the yt-dlp codebase.
+
+## Running Tests
+
+### Using hatch (requires `pip install hatch`)
+
+```bash
+# Run tests for a specific test file
+hatch run hatch-test:run test/test_utils.py
+
+# Run a specific test class or method
+hatch run hatch-test:run test/test_utils.py::TestUtil
+hatch run hatch-test:run test/test_utils.py::TestUtil::test_url_basename
+
+# Run with verbosity
+hatch run hatch-test:run -- test/test_utils.py -v
+```
+
+### Using pytest directly
+
+```bash
+# Run a specific test file
+python -m pytest test/test_utils.py
+
+# Run a specific test class or method
+python -m pytest test/test_utils.py::TestUtil
+python -m pytest test/test_utils.py::TestUtil::test_url_basename
+
+# Run with verbosity
+python -m pytest -v test/test_utils.py
+```
+
+**Important:** Always run tests from the project root directory, not from a subdirectory.
+
+## Code Coverage
+
+For information on running tests with code coverage, see the documentation in `.coverage-reports/README.md`.

test/devscripts/test_install_deps.py

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+import os
+import sys
+import unittest
+from unittest import mock
+
+sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.dirname(os.path.abspath(__file__)))))
+
+from devscripts import install_deps
+
+
+class TestInstallDeps(unittest.TestCase):
+
+    @mock.patch('devscripts.install_deps.parse_toml')
+    @mock.patch('devscripts.install_deps.read_file')
+    @mock.patch('devscripts.install_deps.subprocess.call')
+    def test_print_option(self, mock_call, mock_read_file, mock_parse_toml):
+        # Mock the parse_toml function to return a project table with dependencies
+        mock_parse_toml.return_value = {
+            'project': {
+                'name': 'yt-dlp',
+                'dependencies': ['dep1', 'dep2'],
+                'optional-dependencies': {
+                    'default': ['opt1', 'opt2'],
+                    'test': ['test1', 'test2'],
+                    'dev': ['dev1', 'dev2'],
+                },
+            },
+        }
+
+        # Mock sys.argv to simulate command line arguments
+        with mock.patch('sys.argv', ['install_deps.py', '--print']):
+            # Redirect stdout to capture the output
+            from io import StringIO
+            import sys
+            original_stdout = sys.stdout
+            try:
+                output = StringIO()
+                sys.stdout = output
+
+                # Execute the main function
+                install_deps.main()
+
+                # Get the captured output
+                printed_deps = output.getvalue().strip().split('\n')
+
+                # Check that default dependencies are included
+                # 2 from dependencies + default dependencies
+                self.assertEqual(len(printed_deps), 4)
+                self.assertIn('dep1', printed_deps)
+                self.assertIn('dep2', printed_deps)
+                self.assertIn('opt1', printed_deps)
+                self.assertIn('opt2', printed_deps)
+
+            finally:
+                sys.stdout = original_stdout
+
+        # Call was not made because we used --print
+        mock_call.assert_not_called()
+
+
+if __name__ == '__main__':
+    unittest.main()