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D Tip - Skipping main() for Unit Tests

Posted: 2013-06-11 - Link

When you compile a D program with unit tests enabled (using the -unittest flag), the generated executable will first run the unit tests then continue with executing main().

Sometimes, you just want the unit tests to run in isolation.

A simple way to skip execution of main() for unit test builds is to use the unittest version identifier:

unittest
{
    assert(1 + 1 == 2, "Something horrible has gone wrong.");
}

void main()
{
    version(unittest)
        return;

    // This won't be run
}

Code inside the version(unittest) block will only be run when the code is compiled with -unittest, so the code above will exit main() immediately in unit test builds.

There are numerous pre-defined version identifiers, which you can find at http://dlang.org/version.html. Another handy one is version(assert), which is only compiled in when asserts are enabled.

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