test-lib: Adjust output to be valid TAP format

test-lib: Adjust output to be valid TAP format

TAP, the Test Anything Protocol, is a simple text-based interface
between testing modules in a test harness. test-lib.sh's output was
already very close to being valid TAP. This change brings it all the
way there. Before:

    $ ./t0005-signals.sh
    *   ok 1: sigchain works
    * passed all 1 test(s)

And after:

    $ ./t0005-signals.sh
    ok 1 - sigchain works
    # passed all 1 test(s)
    1..1

The advantage of using TAP is that any program that reads the format
(a "test harness") can run the tests. The most popular of these is the
prove(1) utility that comes with Perl. It can run tests in parallel,
display colored output, format the output to console, file, HTML etc.,
and much more. An example:

    $ prove ./t0005-signals.sh
    ./t0005-signals.sh .. ok
    All tests successful.
    Files=1, Tests=1,  0 wallclock secs ( 0.03 usr  0.00 sys +  0.01 cusr  0.02 csys =  0.06 CPU)
    Result: PASS

prove(1) gives you human readable output without being too
verbose. Running the test suite in parallel with `make test -j15`
produces a flood of text. Running them with `prove -j 15 ./t[0-9]*.sh`
makes it easy to follow what's going on.

All this patch does is re-arrange the output a bit so that it conforms
with the TAP spec, everything that the test suite did before continues
to work. That includes aggregating results in t/test-results/, the
--verbose, --debug and other options for tests, and the test color
output.

TAP harnesses ignore everything that they don't know about, so running
the tests with --verbose works:

    $ prove ./t0005-signals.sh :: --verbose --debug
    ./t0005-signals.sh .. Terminated
    ./t0005-signals.sh .. ok
    All tests successful.
    Files=1, Tests=1,  0 wallclock secs ( 0.02 usr  0.01 sys +  0.01 cusr  0.01 csys =  0.05 CPU)
    Result: PASS

Just supply the -v option to prove itself to get all the verbose
output that it suppresses:

    $ prove -v ./t0005-signals.sh :: --verbose --debug
    ./t0005-signals.sh ..
    Initialized empty Git repository in /home/avar/g/git/t/trash directory.t0005-signals/.git/
    expecting success:
            test-sigchain >actual
            case "$?" in
            143) true ;; # POSIX w/ SIGTERM=15
              3) true ;; # Windows
              *) false ;;
            esac &&
            test_cmp expect actual
    Terminated
    ok 1 - sigchain works
    # passed all 1 test(s)
    1..1
    ok
    All tests successful.
    Files=1, Tests=1,  0 wallclock secs ( 0.02 usr  0.00 sys +  0.01 cusr  0.01 csys =  0.04 CPU)
    Result: PASS

As a further example, consider this test script that uses a lot of
test-lib.sh features by Jakub Narebski:

    #!/bin/sh

    test_description='this is a sample test.

    This test is here to see various test outputs.'

    . ./test-lib.sh

    say 'diagnostic message'

    test_expect_success 'true  test' 'true'
    test_expect_success 'false test' 'false'

    test_expect_failure 'true  test (todo)' 'true'
    test_expect_failure 'false test (todo)' 'false'

    test_debug 'echo "debug message"'

    test_done

The output of that was previously:

    * diagnostic message                      # yellow
    *   ok 1: true  test
    * FAIL 2: false test                      # bold red
            false
    *   FIXED 3: true  test (todo)
    *   still broken 4: false test (todo)     # bold green
    * fixed 1 known breakage(s)               # green
    * still have 1 known breakage(s)          # bold red
    * failed 1 among remaining 3 test(s)      # bold red

But is now:

    diagnostic message                                    # yellow
    ok 1 - true  test
    not ok - 2 false test                                 # bold red
    #       false
    ok 3 - true  test (todo) # TODO known breakage
    not ok 4 - false test (todo) # TODO known breakage    # bold green
    # fixed 1 known breakage(s)                           # green
    # still have 1 known breakage(s)                      # bold red
    # failed 1 among remaining 3 test(s)                  # bold red
    1..4

All the coloring is preserved when the test is run manually. Under
prove(1) the test performs as expected, even with --debug and
--verbose options:

    $ prove ./example.sh :: --debug --verbose
    ./example.sh .. Dubious, test returned 1 (wstat 256, 0x100)
    Failed 1/4 subtests
            (1 TODO test unexpectedly succeeded)

    Test Summary Report
    -------------------
    ./example.sh (Wstat: 256 Tests: 4 Failed: 1)
      Failed test:  2
      TODO passed:   3
      Non-zero exit status: 1
    Files=1, Tests=4,  0 wallclock secs ( 0.02 usr  0.00 sys +  0.00 cusr  0.01 csys =  0.03 CPU)
    Result: FAIL

The TAP harness itself doesn't get confused by the color output, they
aren't used by test-lib.sh stdout isn't open to a terminal (test -t 1).

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>