code: def dataplaceholders(self, simple_step, shared_step):
      x1 = Input(name="x1")
      x2 = Input(name="x2")
      y_t = Input(name="y_t")
      y_simple = simple_step(x1, y_t)
      y_shared_1 = shared_step(x1, y_t)
      y_shared_2 = shared_step(
          x2,
          compute_func="predict_proba",
          fit_compute_func="fit_predict_proba",
          trainable=False,
      )
      return x1, x2, y_t, y_simple, y_shared_1, y_shared_2
  
imports: from contextlib import contextmanager
  from functools import partial
  import pytest
  from sklearn.base import TransformerMixin, BaseEstimator
  from baikal import Input, Step, set_config
  from baikal._core.data_placeholder import DataPlaceholder
  from baikal._core.step import InputStep
  from tests.helpers.fixtures import teardown
  from tests.helpers.dummy_steps import DummyMIMO, DummySISO, DummyEstimator
  from tests.helpers.sklearn_steps import LogisticRegression, PCA
label_desc: Use image node_id 18 for calling the TestStep obj's underlying member method code with example usage: obj.dataplaceholders(simple_step, shared_step) and returns: x1,  x2,  y_t,  y_simple,  y_shared_1,  y_shared_2