TAP support: add functional test to parse TAP with external library

One of the most important points of having TAP support is allowing
other tools to parse the results of the Avocado tests.  IMHO the best
way to test that we're producing sound TAP support is to use stable
implementations for that.

AFAIK, Perl is where TAP was born, and its TAP library is kind of a
reference implementation.  Let's use that, if available, to check if
our tap generation is sound.
Signed-off-by: NCleber Rosa <crosa@redhat.com>
Signed-off-by: NLukáš Doktor <ldoktor@redhat.com>

selftests/functional/test_output.py

@@ -14,11 +14,26 @@ else:
 from avocado.core import exit_codes
 from avocado.core.output import TermSupport
 from avocado.utils import process
+from avocado.utils import script
 
 basedir = os.path.join(os.path.dirname(os.path.abspath(__file__)), '..', '..')
 basedir = os.path.abspath(basedir)
 
 
+PERL_TAP_PARSER_SNIPPET = """#!/bin/env perl
+use TAP::Parser;
+
+my $parser = TAP::Parser->new( { exec => ['./scripts/avocado', 'run', 'passtest.py', 'errortest.py', 'warntest.py', '--tap', '-'] } );
+
+while ( my $result = $parser->next ) {
+        $result->is_unknown && die "Unknown line \\"" . $result->as_string . "\\" in the TAP output!\n";
+}
+$parser->parse_errors == 0 || die "Parser errors!\n";
+$parser->is_good_plan || die "Plan is not a good plan!\n";
+$parser->plan eq '1..3' || die "Plan does not match what was expected!\n";
+"""
+
+
 def image_output_uncapable():
     try:
         import PIL
@@ -27,6 +42,10 @@ def image_output_uncapable():
         return True
 
 
+def perl_tap_parser_uncapable():
+    return os.system("perl -e 'use TAP::Parser;'") != 0
+
+
 class OutputTest(unittest.TestCase):
 
     def setUp(self):
@@ -371,6 +390,15 @@ class OutputPluginTest(unittest.TestCase):
             except OSError:
                 pass
 
+    @unittest.skipIf(perl_tap_parser_uncapable(),
+                     "Uncapable of using Perl TAP::Parser library")
+    def test_tap_parser(self):
+        perl_script = script.TemporaryScript("tap_parser.pl",
+                                             PERL_TAP_PARSER_SNIPPET)
+        perl_script.save()
+        os.chdir(basedir)
+        process.run("perl %s" % perl_script)
+
     def tearDown(self):
         shutil.rmtree(self.tmpdir)