### Body

Currently `start_date` is mandatory parameter.
For DAGs with `schedule=None` we can relax this requirement as no scheduling calculation needed so the `start_date` parameter isn't used.

### Committer

- [X] I acknowledge that I am a maintainer/committer of the Apache Airflow project.
"""
        Test that when 'params' exists as a key passed to the default_args dict
        in addition to params being passed explicitly as an argument to the
        dag, that the 'params' key of the default_args dict is merged with the
        dict of the params argument.
        """
        params1 = {"parameter1": 1}
        params2 = {"parameter2": 2}
        dag = DAG("test-dag", default_args={"params": params1}, params=params2)
        assert params1["parameter1"] == dag.params["parameter1"]
        assert params2["parameter2"] == dag.params["parameter2"]
    def test_not_none_schedule_with_non_default_params(self):
        """
        Test if there is a DAG with not None schedule_interval and have some params that
        don't have a default value raise a error while DAG parsing
        """
        params = {"param1": Param(type="string")}
        with pytest.raises(AirflowException):
            DAG("dummy-dag", params=params)
    def test_dag_invalid_default_view(self):
        """
        Test invalid `default_view` of DAG initialization
        """
        with pytest.raises(AirflowException, match="Invalid values of dag.default_view: only support"):
            DAG(dag_id="test-invalid-default_view", default_view="airflow")
    def test_dag_default_view_default_value(self):