When running tests, it's sometimes helpful to see verbose output from a
test even when it succeeds. This can be useful to compare to a failure
on another system to determine the relevant differences between the
systems. Add support for reading an environment variable,
LFS_DUMP_TEST_OUTPUT, that if set to a nonempty string causes the
verbose test output to be printed. Continue printing verbose output
automatically if an assertion fails.
By default, the prove(1) program looks for tests to run in the 't'
directory at the repository root, so let's put existing tests there in
order to remove a non-default argument from prove.
