We had two classes named `PipeTest`: one in `PipeTestUtilities.h` and
one in `PipeTest.cpp`. The latter was unintentionally using the wrong
class (from the header) which didn't initialize the HostInfo subsystem.
This resulted in a crash due to a nullptr dereference (`g_fields`) when
`PipePosix::CreateWithUniqueName` called `HostInfoBase::GetProcessTempDir`.
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