Issue 3422 refactor testdata consts

[martgil]

This PR will remove testdata.json and move its contents to const.ts

close #3422 // if this PR closes an issue

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Tests (delete all except exactly one):

• Difficult to test (explain why)
• Not worth testing
• Tests will be added later (issue #...)
• Tests added or updated

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To be filled by reviewers

I have reviewed that this PR... (tick whichever items you personally focused on during this review):

• addresses the issue it closes (if any)
• code is readable and understandable
• is accompanied with tests, or tests are not needed
• is free of vulnerabilities
• is documented clearly and usefully, or doesn't need documentation