[t] Add a basic test for a passing exit code

Trying to debug this:

(kadath)(~/git/tapir master )$ ~/svn/parrot/parrot t/harness.pir t/*.t
t/00-sanity.t ................. failed 0/0 tests, exit code = 1
t/01-parse_plan.t ............. failed 0/0 tests, exit code = 1
t/02-parse_tapstream.t ........ failed 0/0 tests, exit code = 1
t/03-parse_tapstream_error.t .. failed 0/0 tests, exit code = 1
FAILED 4 test(s) in 4/4 files

t/03-parse_tapstream_error.t

@@ -7,7 +7,7 @@
     .include 'test_more.pir'
     .local pmc tapir, klass
 
-    plan(27)
+    plan(28)
 
     # setup test data
     klass = newclass [ 'Tapir'; 'Parser' ]
@@ -17,8 +17,24 @@
     test_parse_death_with_passing_tests(tapir)
     test_plumage_sanity(tapir)
     test_exit_code(tapir)
+    test_exit_code_pass(tapir)
 .end
 
+.sub test_exit_code_pass
+    .param pmc tapir
+    .local string tap
+    .local pmc stream
+    tap = <<"TAP"
+1..2
+ok 1 - Class of Tapir::Parser is of the correct type
+ok 2 - new returns a Tapir::Parser object isa Tapir;Parser
+TAP
+    stream = tapir.'parse_tapstream'(tap,0)
+    $I0 = stream.'get_exit_code'()
+    is($I0,0,"parse_tapstream gets passing exit code")
+.end
+
+
 .sub test_exit_code
     .param pmc tapir
     .local string tap_error