I think that Phobos shouldn't declare public symbols in version(unittest) blocks, as these can conflict with unittests in user code. Many of them have names that are unlikely to appear in user code. But others are quite common (e.g. Length, in std.range). See attached list for a quickly generated list of such symbols.
Comment #1 by dransic — 2014-01-21T09:54:45Z
Created attachment 1315
List of public unittest symbols
Comment #2 by github-bugzilla — 2018-08-26T20:56:49Z