Too many (separate) tests?

There may be to many individual test binaries which slow down the build/CI. See e.g. https://github.com/boostorg/unordered/runs/6779803837?check_suite_focus=true

For `b2 -j3 libs/%LIBRARY%/test toolset=msvc-14.3 cxxstd=14,17,20,latest address-model=32,64 variant=debug,release embed-manifest-via=linker` it already yields (at least) 4*2*2=16 variants of each test.

In the test Jamfile we have 54 run-tests and 4 compile-tests yielding at least 928 compilations. That job already takes over an hour on GHA. With coverage collection it is even over 3h and counting.

And it seems the calculation is still to low: `...updated 7154 targets...` O.o

Is it possible to trim that down? E.g. combine more tests into single compilation units as especially on Windows firing up the compiler/linker is very expensive (in terms of time).

Also I'm not sure where the additional factor of 7 (in the targets) is coming from. Maybe that could also be trimmed down somehow.

Start with the test Jamfile and the supplied b2 command, then inspect the linked GitHub Actions run to compare test variants, compilations, and reported targets. Determine where the extra targets come from and identify which test binaries or variants can be combined without losing coverage; done means a reduced build workload with the existing tests still running.

Written by the indexing model from the issue text.