[Python] While testing with airflow, to see task.run, task.execute but I got an error

While testing airflow with pytest, i got an Error.

import datetime
import pytest

from airflow.models import BaseOperator, TaskInstance
from airflow.models.dag import DAG
from airflow.utils.types import DagRunType
from airflow.utils.state import DagRunState, TaskInstanceState
from airflow.utils import timezone

class SampleOperator(BaseOperator):
template_fields = ("_start_date", "_end_date")

def __init__(self, start_date, end_date, **kwargs):
super().__init__(**kwargs)
self._start_date = start_date
self._end_date = end_date

def execute(self, context):
return context

@pytest.fixture
def dag():
with DAG(
dag_id="test_dag_id",
schedule=None,
default_args={
"owner": "airflow",
"start_date": datetime.datetime(2025, 4, 5),
"end_date": datetime.datetime(2025, 4, 6)
}
) as dag:

SampleOperator(
task_id="test_task_id",
start_date="{{ prev_ds }}",
end_date="{{ ds }}"
)

return dag


def test_execute(dag):
run_id = f"test_run_id"
dagrun = dag.create_dagrun(
data_interval=(
dag.default_args["start_date"],
dag.default_args["end_date"]
),
run_id=run_id,
start_date=dag.default_args["end_date"],
state=DagRunState.RUNNING,
run_type=DagRunType.MANUAL
)

ti = dagrun.get_task_instance(task_id="test_task_id")
assert ti is not None # error here, ti is None



But task is None My airflow version is 2.10.5

Here is the Error

ti = dagrun.get_task_instance(task_id="test_task_id")
> assert ti is not None
E assert None is not None

tests/test_instance_context.py:59: AssertionError


I referenced the code https://airflow.apache.org/docs/apache-airflow/2.10.5/best-practices.html#testing-a-dag

But I don't know why..

I want to test task.run to see difference between task.run and task.execute. when I passed jinja variables, then airflow automatically rendering the variables by run method.

So, I want to see prev_ds, ds, start_date, end_date is successfully rendered. But I got an error above..

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