Original README.TESTS from one-true-awk regdir tests directory:
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The archive of test files contains 

- A shell file called REGRESS that controls the testing process.

- Several shell files called Compare* that control sub-parts
of the testing.

- About 160 small tests called t.* that constitute a random
sampling of awk constructions collected over the years.
Not organized, but they touch almost everything.

- About 60 small tests called p.* that come from the first
two chapters of The AWK Programming Environment.  This is
basic stuff -- they have to work.

These two sets are intended as regression tests, to be sure
that a new version produces the same results as a previous one.
There are a couple of standard data files used with them,
test.data and test.countries, but others would work too.

- About 20 files called T.* that are self-contained and
more systematic tests of specific language features.
For example, T.clv tests command-line variable handling.
These tests are not regressions -- they compute the right
answer by separate means, then compare the awk output.
A specific test for each new bug found shows up in at least
one of these, most often T.misc.  There are about 220 tests
total in these files.

- Two of these files, T.re and T.sub, are systematic tests
of the regular expression and substitution code.  They express
tests in a small language, then generate awk programs that
verify behavior.

- About 20 files called tt.* that are used as timing tests;
they use the most common awk constructions in straightforward
ways, against a large input file constructed by Compare.tt.


There is undoubtedly more stuff in the archive;  it's been
collecting for years and may need pruning.  Suggestions for
improvement, additional tests (especially systematic ones),
and the like are all welcome.

