doc: load with an instance of TaskOnKart

docs/task_on_kart.rst

@@ -147,6 +147,15 @@ The `load` method loads individual task input by passing a key of an input dicti
         data_b = self.load('b')
 
 
+As an alternative, the `load` method loads individual task input by passing an instance of TaskOnKart as follows:
+
+.. code:: python
+
+    def run(self):
+        data_a = self.load(TaskA())
+        data_b = self.load(TaskB())
+
+
 We can also omit the :func:`~gokart.task.TaskOnKart.requires` and write the task used by :func:`~gokart.parameter.TaskInstanceParameter`.
 Extensions include :func:`~gokart.task.TaskOnKart.load_data_frame` and :func:`~gokart.task.TaskOnKart.load_generator`. Please refer to :func:`~gokart.task.TaskOnKart.load`, :doc:`task_parameters`, and described later Advanced Features section.
 

test/test_build.py

@@ -57,6 +57,17 @@ def run(self):
         self.dump('done')
 
 
+class _LoadRequires(gokart.TaskOnKart[None]):
+    task: _DummyTask = gokart.TaskInstanceParameter()
+
+    def requires(self):
+        return self.task
+
+    def run(self):
+        _ = self.load(self.task)
+        self.dump(None)
+
+
 class RunTest(unittest.TestCase):
     def setUp(self):
         luigi.setup_logging.DaemonLogging._configured = False
@@ -102,6 +113,11 @@ def test_failed_task(self):
         with self.assertRaises(GokartBuildError):
             gokart.build(_DummyFailedTask(), reset_register=False, log_level=logging.CRITICAL)
 
+    def test_load_requires(self):
+        text = 'test'
+        output = gokart.build(_LoadRequires(task=_DummyTask(param=text)), reset_register=False)
+        self.assertEqual(output, None)
+
 
 class LoggerConfigTest(unittest.TestCase):
     def test_logger_config(self):