c84c2b8c92 tests: Test for expected return values when calling functions returning a success code (practicalswift)
Pull request description:
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
$
```
---
Backport of Core [[https://github.com/bitcoin/bitcoin/pull/14935 | PR14935]]