Make failing tests possible, improve test output.

[kaeluka]

Until now it has been possible to test only that something succeeds
(specifically, that the output matches exactly). This limited the
tests to cases where we had determinism and where the expected output
was exactly known.

This commit extends test.sh to maintain the old functionality, but now
ALSO allows checking scripts to be used instead of the old .out files.

A checking script is an executable whose name is that of a test, but
with the ending .chk -- if the test source if called foo.enc, the
checking script is called foo.chk and it is executable. The file
testutils.sh contains a few functions to make it easier to write tests
and to make maintenance of tests easier, should error output change
(then only this file has to be updated).

The make test command will now compile foo.enc and try to run it
(if compilation succeeds). The output of both compilation and
execution will be piped into the checking script. The checking script
can analyse the input and return successfully to signal that
everything is ok, or with a failure code to signal an error.

An example:

File fail.enc:

class Main
  def main() : void
    repeat i <- 100 {
      print x -- error should occur here
    }

File fail.chk:

#!/usr/bin/env bash
source testutils.sh

error_at 4
error_msg "Unbound variable 'x'"

[kaeluka]

This is a new pull request (instead of #121), with a small testing lib that'll make writing tests clearer and easier.

[TheGrandmother]

👍
This is great!