Support expectations have more nested expectations that can match.

master/buildbot/test/fake/remotecommand.py

@@ -279,6 +279,12 @@ def shouldKeepMatchingAfter(self, command):
         """
         return False
 
+    def nestedExpectations(self):
+        """
+        Any sub-expectations that should be validated.
+        """
+        return []
+
     def __repr__(self):
         return "Expect(" + repr(self.remote_command) + ")"
 

master/buildbot/test/util/steps.py

@@ -322,6 +322,18 @@ def check(result):
     def _validate_expectation(self, exp, command):
         got = (command.remote_command, command.args)
 
+        for child_exp in exp.nestedExpectations():
+            try:
+                yield self._validate_expectation(child_exp, command)
+                exp.expectationPassed(exp)
+            except AssertionError as e:
+                # log this error, as the step may swallow the AssertionError or
+                # otherwise obscure the failure.  Trial will see the exception in
+                # the log and print an [ERROR].  This may result in
+                # double-reporting, but that's better than non-reporting!
+                log.err()
+                exp.raiseExpectationFailure(child_exp, e)
+
         if exp.shouldAssertCommandEqualExpectation():
             # handle any incomparable args
             for arg in exp.incomparable_args: