A sample unit test for a Python DAG.

## Code sample

### Python


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    from airflow import models
    from airflow.utils.dag_cycle_tester import test_cycle


    def assert_has_valid_dag(module):
        """Assert that a module contains a valid DAG."""

        no_dag_found = True

        for dag in vars(module).values():
            if isinstance(dag, models.DAG):
                no_dag_found = False
                test_cycle(dag)  # Throws if a task cycle is found.

        if no_dag_found:
            raise AssertionError("module does not contain a valid DAG")

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