demo/exit-code.should, src/should.py: test non-zero exit codes

closes #31

demo/exit-code.should

@@ -2,9 +2,14 @@
 # Other exit codes can be given
 
 # The files differ
+$ Exit code is exactly '1'
 !EXIT_CODE: 1
 diff demo/hello.should demo/cal.should
 
+$ Exit code is not zero
+!EXIT_CODE: +
+diff demo/hello.should demo/cal.should
+
 $ 'world' is in the diff
 : world
 

src/should.py

@@ -817,7 +817,8 @@ class TestSuite():
 
             # Directive -- Exit code
             if l.startswith(DIRECTIVE_EXIT_CODE):
-                self.expected_exit_code = int(l[len(DIRECTIVE_EXIT_CODE):].strip())
+                e = l[len(DIRECTIVE_EXIT_CODE):].strip()
+                self.expected_exit_code = NOT_ZERO if e == NOT_ZERO else int(e)
                 continue
 
             # Name
@@ -904,11 +905,15 @@ class TestSuite():
                              stdout=f_stdout, stderr=f_stderr,
                              close_fds=True)
 
-        exit_code_message = 'Exit code is %d -- %s' % (self.expected_exit_code, cmd)
+        exit_code_message = 'Exit code is %s -- %s' % (self.expected_exit_code, cmd)
 
         try:
             self.exit_code = p.wait(self.timeout)
-            exit_test = ExternalTestCase(exit_code_message, self.exit_code == self.expected_exit_code, str(self.exit_code))
+            if self.expected_exit_code == NOT_ZERO:
+                success = (self.exit_code > 0)
+            else:
+                success = (self.exit_code == self.expected_exit_code)
+            exit_test = ExternalTestCase(exit_code_message, success, str(self.exit_code))
         except subprocess.TimeoutExpired:
             self.exit_code = None
             exit_test = ExternalTestCase(exit_code_message, S_SKIP, 'timeout after %s seconds' % self.timeout)