autotest: use message hook when waiting for statustext

Eliminates a race condition when waiting for statustexts.  Getting the
current sim time slurps messages.

Tools/autotest/common.py

@@ -126,6 +126,7 @@ class Context(object):
     def __init__(self):
         self.parameters = []
         self.sitl_commandline_customised = False
+        self.message_hooks = []
 
 # https://stackoverflow.com/questions/616645/how-do-i-duplicate-sys-stdout-to-a-log-file-in-python
 class TeeBoth(object):
@@ -2142,6 +2143,12 @@ class AutoTest(ABC):
     def install_message_hook(self, hook):
         self.mav.message_hooks.append(hook)
 
+    def install_message_hook_context(self, hook):
+        '''installs a message hook which will be removed when the context goes
+        away'''
+        self.mav.message_hooks.append(hook)
+        self.context_get().message_hooks.append(hook)
+
     def remove_message_hook(self, hook):
         oldlen = len(self.mav.message_hooks)
         self.mav.message_hooks = list(filter(lambda x : x != hook,
@@ -2938,6 +2945,8 @@ class AutoTest(ABC):
             self.set_parameter(name,
                                old_value,
                                add_to_context=False)
+        for hook in dead.message_hooks:
+            self.remove_message_hook(hook)
 
     class Context(object):
         def __init__(self, testsuite):
@@ -3841,18 +3850,32 @@ Also, ignores heartbeats not from our target system'''
         self.wait_statustext(*args, **kwargs)
 
     def wait_statustext(self, text, timeout=20, the_function=None):
-        """Wait a specific STATUS_TEXT."""
+        """Wait for a specific STATUSTEXT."""
+
+        # Statustexts are often triggered by something we've just
+        # done, so we have to be careful not to read any traffic that
+        # isn't checked for being our statustext.  That doesn't work
+        # well with getting the curent simulation time (which requires
+        # a new SYSTEM_TIME message), so we install a message hook
+        # which checks all incoming messages.
         self.progress("Waiting for text : %s" % text.lower())
+        global statustext_found
+        statustext_found = False
+        def mh(mav, m):
+            global statustext_found
+            if m.get_type() != "STATUSTEXT":
+                return
+            if text.lower() in m.text.lower():
+                self.progress("Received expected text : %s" % m.text.lower())
+                statustext_found = True
+        self.install_message_hook_context(mh)
         tstart = self.get_sim_time()
         while self.get_sim_time_cached() < tstart + timeout:
+            if statustext_found:
+                return
             if the_function is not None:
                 the_function()
             m = self.mav.recv_match(type='STATUSTEXT', blocking=True, timeout=0.1)
-            if m is None:
-                continue
-            if text.lower() in m.text.lower():
-                self.progress("Received expected text : %s" % m.text.lower())
-                return True
         raise AutoTestTimeoutException("Failed to received text : %s" %
                                        text.lower())