code: def test_valid_string_strategy(self):
      with pm.Model() as pmodel:
          pm.Uniform("x", 0, 1, size=2, initval="unknown")
          with pytest.raises(
              ValueError, match="Invalid string strategy: unknown"
          ):
              pmodel.initial_point(random_seed=0)
  
imports: import cloudpickle
  import numpy
  import pytensor
  import pytensor.tensor
  import pytest
  from pytensor.tensor.random.op import RandomVariable
  import pymc
  from pymc.distributions.distribution import moment
  from pymc.initial_point import make_initial_point_fn, make_initial_point_fns_per_chain
label_desc: Use image node_id 3 for calling the TestInitvalAssignment obj's underlying member method code with example usage: obj.test_valid_string_strategy() without return types