Rename old fake BackendV2 classes

[HuangJunye]

What is the expected enhancement?

#7643 implemented mocked IBM Quantum Systems backends using the new BackendV2 interface.

There were older fake BackendV2 classes that were created before for testing. We need to rename, reorganize or remove those classes

https://github.com/Qiskit/qiskit-terra/blob/8105a80c84ce2447a1e224b85f4f56e98f074763/qiskit/test/mock/fake_mumbai_v2.py

• FakeMumbaiV2. Fixed by Rename old FakeMumbaiV2 to avoid name conflict with new FakeMumbaiV2 #7839

https://github.com/Qiskit/qiskit-terra/blob/8105a80c84ce2447a1e224b85f4f56e98f074763/qiskit/test/mock/fake_backend_v2.py

• FakeBackendV2
• FakeBackend5QV2
• FakeBackendSimple

[HuangJunye]

Reopening as #7839 only partially fixed this issue.

[HuangJunye]

@mtreinish What would you suggest to replace the old FakeBackendV2 class? Should I choose one of the fake IBM Quantum systems to replace it, e.g. FakeMumbaiV2? And use a FakeBelemV2 to replace the usage of FakeBackend5QV2?

[HuangJunye]

I decided to use FakeManilaV2 which has 5Q qubits to replace FakeBackendV2, FakeBackend5QV2 and FakeBackendSimple. One thing I am not sure is how to deal with FakeBackendV2LegacyQubitProps.

https://github.com/Qiskit/qiskit-terra/blob/main/qiskit/test/mock/fake_backend_v2.py#L103-L109

[HuangJunye]

@mtreinish Having a deeper look at the different classes of these fake backends.

FakeBackendSimple is only used in https://github.com/Qiskit/qiskit-terra/blob/main/test/python/algorithms/test_backendv2.py and https://github.com/Qiskit/qiskit-terra/blob/6aacabd99122be2c2d59ef29655217db6ab33f0f/test/python/providers/test_backend_v2.py#L68-L71 so I can probably replace it with a fake V2 IBM Quantum backend with more than 18 qubits (required for the shor factoring test) or (probably better approach) a fake V2 QasmSimulator.

The rest of them are written in a very specific way and the tests specifically test the details of these backends. I am not sure how to generalize them to base on the new FakeBackendV2 or a specific instance of a fake V2 IBM Quantum backend.

Or maybe I should just rename them and improve docstrings to describe what they are used for?

[1ucian0]

I think this is can be closed, via #10918