e2etests: we are able to receive optional stanzas

tests/end_to_end/__main__.py

@@ -21,6 +21,17 @@ class MatchAll(MatcherBase):
 
 
 class StanzaError(Exception):
+    """
+    Raised when a step fails.
+    """
+    pass
+
+
+class SkipStepError(Exception):
+    """
+    Raised by a step when it needs to be skiped, by running
+    the next available step immediately.
+    """
     pass
 
 
@@ -69,6 +80,10 @@ class XMPPComponent(slixmpp.BaseXMPP):
                 self.stanza_checker(stanza)
             except StanzaError as e:
                 self.error(e)
+            except SkipStepError:
+                # Run the next step and then re-handle this same stanza
+                self.run_scenario()
+                return self.handle_incoming_stanza(stanza)
             self.stanza_checker = None
         self.run_scenario()
 
@@ -97,6 +112,13 @@ def check_xpath(xpaths, stanza):
             raise StanzaError("Received stanza “%s” did not match expected xpath “%s”" % (stanza, xpath))
 
 
+def check_xpath_optional(xpaths, stanza):
+    try:
+        check_xpath(xpaths, stanza)
+    except StanzaError:
+        raise SkipStepError()
+
+
 class Scenario:
     """Defines a list of actions that are executed in sequence, until one of
     them throws an exception, or until the end.  An action can be something
@@ -170,11 +192,12 @@ def send_stanza(stanza, xmpp, biboumi):
     asyncio.get_event_loop().call_soon(xmpp.run_scenario)
 
 
-def expect_stanza(xpaths, xmpp, biboumi):
+def expect_stanza(xpaths, xmpp, biboumi, optional=False):
+    check_func = check_xpath if not optional else check_xpath_optional
     if isinstance(xpaths, str):
-        xmpp.stanza_checker = partial(check_xpath, [xpaths.format_map(common_replacements)])
+        xmpp.stanza_checker = partial(check_func, [xpaths.format_map(common_replacements)])
     elif isinstance(xpaths, tuple):
-        xmpp.stanza_checker = partial(check_xpath, [xpath.format_map(common_replacements) for xpath in xpaths])
+        xmpp.stanza_checker = partial(check_func, [xpath.format_map(common_replacements) for xpath in xpaths])
     else:
         print("Warning, from argument type passed to expect_stanza: %s" % (type(xpaths)))