Tests fail to collect with ddt==1.4.3

[jakelishman]

Information

• Qiskit Terra version: any
• Python version: any
• Operating system: any

What is the current behavior?

The test suite may fail to collect now for all OSes on CI, due to the new ddt version 1.4.3 (released about an hour ago). This appears related to datadriventests/ddt#92 - the signature of ddt.idata changed in a backwards-incompatible manner, and there's no way to support both signatures idata(iterable) and idata(iterable, length) cleanly.

Steps to reproduce the problem

Run the test suite with ddt=1.4.3.

What is the expected behavior?

Tests do not fail to collect.

Suggested solutions

Arguably this is a bug/mishandling of the user interface in ddt, but we can work around it by either forbidding use of ddt=1.4.3 in constraints.txt, or swapping all uses of ddt.idata(iterable) to ddt.data(*iterable).

[jakelishman]

Having looked into it a bit closer, I think this is a slight "interface bug" in ddt, and the best thing for us to do is just disallow ddt==1.4.3 in the constraints, and I'll work with the ddt team to see if we can have an interface fix merged upstream. For now, see datadriventests/ddt#97.