code: def test_dropout_requires_key(self):
      mod = mlp.MLP([1, 1])
      with self.assertRaisesRegex(ValueError, "rng key must be passed"):
          mod(jnp.ones([1, 1]), dropout_rate=0.5)
  
imports: from absl.testing import absltest
  from absl.testing import parameterized
  from haiku._src import test_utils
  from haiku._src.nets import mlp
  import jax
  import jax.numpy
label_desc: Use image node_id 18 for calling the MLPTest obj's underlying member method code with example usage: obj.test_dropout_requires_key() without return types