Unit Tests for CGraph

[tachukao]

As discussed in #531, we should add an unit test module for CGraph. Although most of the operations are defined in Algodiff, we should have unit tests for the init, shape, and optimization functions.
Any ideas on how to best test for these @pvdhove @ryanrhymes @mseri @jzstark ?

[ryanrhymes]

Probably the tests can be divided into several groups.

• Basic operations like adding, removing, modifying nodes.
• Shape inference functions.
• Structural optimisation functions.
• Anything esle?

open to criticisms :)

[jzstark]

Agree. The optimiser and shape interence tests in TensorFlow might be of help, such as optimizer_cse_test.cc, constant_folding_test.cc, shape_inference_test.cc, etc.