docstr: Test initialization with a very long name.
docstr_tok: ["Test","initialization","with","a","very","long","name","."]
code: def test_very_long_name(self):
      """Test initialization with a very long name."""
      with self.assertRaisesRegex(ValueError, "Cannot convert"):
          DTypePolicy("mixed_float16" * 100)
  
imports: from keras.mixed_precision import DTypePolicy
  from keras.mixed_precision import dtype_policy
  from keras.mixed_precision import set_dtype_policy
  from keras.testing import test_case
label_desc: Use image node_id 3 for calling the DTypePolicyEdgeCasesTest obj's underlying member method code with example usage: obj.test_very_long_name() without return types