tests: Test for expected return values when calling functions returning a success code #14935

Test for expected return values when calling functions returning a success code (instead of discarding the return values).

Note to reviewers: The following commands can be used to verify that the only text fragments added in this PR are BOOST_CHECK(, ! and ) :

$ git diff HEAD~1 | grep -E '^[\-][^\-]' | cut -b2- > before.txt
$ git diff HEAD~1 | grep -E '^[\+][^\+]' | cut -b2- > after.txt
$ cat after.txt | sed 's/BOOST_CHECK(//g' | sed 's/));/);/g' | tr -d '!' > after-sed.txt
$ diff -u before.txt after-sed.txt
$ 

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The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

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Conflicts

Reviewers, this pull request conflicts with the following ones:

• #14908 (test: Removed implicit CTransaction constructor calls from tests and benchmarks. by lucash-dev)
• #14906 (refactor: Make explicit CMutableTransaction -> CTransaction conversion. by lucash-dev)

If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

Rebased!

Agree that this improves the tests; ignoring return status is careless.

utACK c84c2b8c92eb56b3b3793fc95265158f5eeb00db