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
$
```

ninja check