Restore test for upgrading v2 to v3

[wojtek-coreum]

Description

I need this to test bdjuno proposal bugs

Reviewers checklist:

• Try to write more meaningful comments with clear actions to be taken.
• Nit-picking should be unblocking. Focus on core issues.

Authors checklist

• Provide a concise and meaningful description
• Review the code yourself first, before making the PR.
• Annotate your PR in places that require explanation.
• Think and try to split the PR to smaller PR if it is big.

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This change is 

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (007ad03) 33.14% compared to head (f7034d5) 33.14%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #760   +/-   ##
=======================================
  Coverage   33.14%   33.14%           
=======================================
  Files         169      169           
  Lines       48122    48122           
=======================================
  Hits        15948    15948           
  Misses      29145    29145           
  Partials     3029     3029           

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[miladz68]

Reviewed 1 of 1 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @dzmitryhil and @ysv)

[ysv]

Reviewed 1 of 1 files at r1, all commit messages.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @dzmitryhil and @wojtek-coreum)

a discussion (no related file):
I'm not sure we need to keep all these tests & legacy code.
Do you need it just to test bdjuno & explorer ?

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[wojtek-coreum]

Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @dzmitryhil and @ysv)

a discussion (no related file):

Previously, ysv (Yaroslav Savchuk) wrote…

I'm not sure we need to keep all these tests & legacy code.
Do you need it just to test bdjuno & explorer ?

Yes, and I don't want to add every time we find bdjuno not working correctly. Let's keep it for some time, then we may remove.

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[ysv]

Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @dzmitryhil)