Update random array from test_stepsizes.TestStepSizeBB.test_bb_converge

[hrobarts]

Changes

test_stepsizes.TestStepSizeBB.test_bb_converge failed in windows because of random array, this PR updates to a fixed array

Testing you performed

Please add any demo scripts to https://github.com/TomographicImaging/CIL-Demos/tree/main/misc

Related issues/links

Closes #2064

Checklist

• I have performed a self-review of my code
• I have added docstrings in line with the guidance in the developer guide
• I have updated the relevant documentation
• I have implemented unit tests that cover any new or modified functionality
• CHANGELOG.md has been updated with any functionality change
• Request review from all relevant developers
• Change pull request label to 'Waiting for review'

Contribution Notes

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• The content of this Pull Request (the Contribution) is intentionally submitted for inclusion in CIL (the Work) under the terms and conditions of the Apache-2.0 License
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[paskino]

I think that the test_bb_converge is a tricky test.

For one, it is a functional test and you are testing that 2 algorithms converge to the same solution with some accuracy without reaching convergence (i.e. infinite iterations).

I would say that a better check would be to:

1. get the reference solution, for instance by pre-running GD with 1/f.L or maybe 2/f.L with a lot of iterations and hard code the solution. I think you could just impose the solution by setting A and x and calculating b.
2. Compare the solution to the reference solution. The test could be that within 80 iterations you want to be below a certain threshold