[Issue 20526] Compiling a program without unit tests with "-unittest" prints "1 unittests passed"

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20526

--- Comment #1 from ZombineDev <petar.p.kirov at gmail.com> ---
The problem in the example snippet could be solved in phobos by guarding all
nested unit tests with `version (StdUnittest)`, but I'm looking for a solution
at the dmd/druntime level, as obviously this affects third-party libraries and
not just phobos.

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