import std.stdio;

pure nothrow:

int foo(int z) { return z*2; }

unittest {	
    writeln("testing foo");
    assert(foo(4) == 8);
}

---
This won't compile, because the unit test calls writeln which is impure and may throw. 

It makes no sense for a unittest to be nothrow. And it's really a nuisance.

And if a unittest isn't conceptually pure, you have a big problem anyway -- the program behaviour will change depending on whether unittests are run, or not.

PATCH: func.c, around line 3460

void UnitTestDeclaration::semantic(Scope *sc)
{
    if (global.params.useUnitTests)
    {
        if (!type)
            type = new TypeFunction(NULL, Type::tvoid, FALSE, LINKd);
        Scope *sc2 = sc->push();
+        // It makes no sense for unit tests to be pure or nothrow.
+        sc2->stc &= ~(STCnothrow | STCpure);
        sc2->linkage = LINKd;
        FuncDeclaration::semantic(sc2);
        sc2->pop();
    }