code: def testFlattenTensorsShapesDefined(self):
      x = array_ops.placeholder(types_pb2.DT_FLOAT, [None])
      with self.assertRaisesRegex(
          ValueError, "must have statically known shape"
      ):
          ar._flatten_tensors([x, x])
  
imports: import time
  import numpy
  from tensorflow.core.framework import types_pb2
  from tensorflow.python.distribute.v1 import all_reduce
  from tensorflow.python.framework import constant_op
  from tensorflow.python.framework import ops
  from tensorflow.python.framework import tensor_shape
  from tensorflow.python.framework import test_util
  from tensorflow.python.ops import array_ops
  from tensorflow.python.ops import math_ops
  from tensorflow.python.ops import state_ops
  from tensorflow.python.platform import test
  from tensorflow.python.platform import tf_logging
label_desc: Use image node_id 1 for calling the AllReduceTest obj's underlying member method code with example usage: obj.testFlattenTensorsShapesDefined() without return types