[lmi] How did this unit test fail?

[Greg Chicares]

When I tested my last set of commits carefully before pushing, I was
really surprised to see that 'bourn_cast_test' failed (without the
change that I sneaked into 'bourn_cast_test.cpp' in commit 3d3e2b6).
Reverting those changes to that file only, which amount only to this:

-    stifle_warning_for_unused_variable(z);
+    (void)&z;

in two places, reproduces the error, which is:

???? test failed:
???? test failed: 0
[invoked from file /opt/lmi/src/lmi/bourn_cast_test.cpp, line: 781]
[file /opt/lmi/src/lmi/bourn_cast_test.cpp, line 261]

The relevant lines are:

260    INVOKE_BOOST_TEST(!std::signbit(bourn_cast<To>( From(0))), file, line);
261    INVOKE_BOOST_TEST( std::signbit(bourn_cast<To>(-From(0))), file, line);

780    test_floating_conversions<double     , long double>(__FILE__, __LINE__);
781    test_floating_conversions<long double, float      >(__FILE__, __LINE__);
782    test_floating_conversions<long double, double     >(__FILE__, __LINE__);

so apparently -0.0L no longer converts to -0.0F.

The only "explanation" I can come up with is the 'miscellany.hpp'
change in that commit somehow broke the test. The only change that
seems relevant is that I #included <limits> and used min() and max()
in an inline ctor for class minmax (which isn't used by bourn_cast<>
or its system test).

Accordingly, my first attempt at circumventing the test failure was to

(1) write stifle_warning_for_unused_variable() inline instead of using
it directly in 'bourn_cast_test.cpp' (as in 3d3e2b6); and

(2) remove "#include miscellany.hpp" from 'bourn_cast_test.cpp'.

That worked: the test no longer failed. Supposing that including the
<limits> header was the problem, I tried #including it in the unit-
test TU...and that didn't make the test fail. Then I tried including
"miscellany.hpp"--i.e., making change (1) but not change (2) above--
and even that didn't make the test fail.

Anyway, I committed it with (1) only, because that's the minimal
change that doesn't break the unit test. I suppose I could separate
class minmax out into its own header independent of "miscellany.hpp",
but I don't like voodoo workarounds for problems I don't understand.

Vadim--I can't guess what went wrong here. Can you see it?