Builds the test map mix affected.files and mix affected.test select
with, at _build/test/mix_affected/test_map.etf or --map <path>. Those
tasks build it themselves when it is missing. Run with MIX_ENV=test.
Compiles the project and starts it as mix test does, requires
test_helper.exs and every test file with a compiler tracer registered,
and runs no test. See MixAffected.TestMap.Builder for the fallbacks when
a test file fails to require, or declares an affected_by glob that is
malformed or names a directory (that file always runs, with a warning). A
summary goes to stderr.
Exit status: 0 when written, 1 on a usage error (including an umbrella root, which is not supported), 2 when the map could not be built.