code: def test_flatten(self):
      # Test that we flatten multiple Composite.
      x, y, z = inputs()
      C = Composite([x, y], [x + y])
      CC = Composite([x, y], [C(x * y, y)])
      assert not isinstance(CC.outputs[0].owner.op, Composite)
  
      # Test with multiple outputs
      CC = Composite([x, y, z], [C(x * y, y), C(x * z, y)])
      # We don't flatten that case.
      assert isinstance(CC.outputs[0].owner.op, Composite)
  
imports: from __future__ import absolute_import, print_function, division
  import unittest
  import numpy
  import theano
  from theano.gof import FunctionGraph
  from theano import gof
  from theano.tests import unittest_tools
  from theano.scalar.basic import floats, float16, float32, float64, ints, int8, int32, complex64, uint8, ComplexError, IntDiv, TrueDiv, Composite, add, div_proxy, and_, eq, neq, invert, mul, Scalar, InRange, cast, constant, switch
  from theano.scalar.basic import true_div, inv, log, log2, log10, log1p, exp, exp2, expm1, sqrt, deg2rad, rad2deg, cos, arccos, sin, arcsin, tan, arctan, arctan2, cosh, arccosh, sinh, arcsinh, tanh, arctanh
label_desc: Use image node_id 3 for calling the test_composite obj's underlying member method code with example usage: obj.test_flatten() without return types