Run tests and show test coverage report.

def coverage():
    """Run tests and show test coverage report."""
    try:
        import pytest_cov  # NOQA
    except ImportError:
        print_failure_message(
            'Install the pytest coverage plugin to use this task, '
            "i.e., `pip install pytest-cov'.")
        raise SystemExit(1)
    import pytest
    pytest.main(PYTEST_FLAGS + [
        '--cov', CODE_DIRECTORY,
        '--cov-report', 'term-missing',
        '--junit-xml', 'test-report.xml',
        TESTS_DIRECTORY])