Don't mask unit test failure
Don't mask unit test failure

Previously we were using the `wait` bash builtin after spinning up
a subprocess for every unit test. The caused only the last process'
exit value to be used for the `make` exit value [1], other unit tests
would be ignored.

[1] Per `man bash` for `wait`: "...the return status is the exit status
                                of the last process or job waited for."

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