More work on the tests...

gpiozero/pins/mock.py

@@ -8,7 +8,7 @@ str = type('')
 
 
 from collections import namedtuple
-from time import time
+from time import time, sleep
 from threading import Thread, Event
 try:
     from math import isclose
@@ -182,7 +182,7 @@ class MockChargingPin(MockPin):
     """
     def __init__(self, number):
         super(MockChargingPin, self).__init__()
-        self.charge_time = 0.01
+        self.charge_time = 0.01 # dark charging time
         self._charge_stop = Event()
         self._charge_thread = None
 
@@ -193,16 +193,51 @@ class MockChargingPin(MockPin):
                 self._charge_stop.set()
                 self._charge_thread.join()
             self._charge_stop.clear()
-            self._charge_thread = Thread(target=lambda: self._charged)
+            self._charge_thread = Thread(target=self._charge)
             self._charge_thread.start()
         elif value == 'output':
-            if self.charge_thread:
+            if self._charge_thread:
                 self._charge_stop.set()
                 self._charge_thread.join()
 
-    def _charged(self):
+    def _charge(self):
         if not self._charge_stop.wait(self.charge_time):
-            self.drive_high()
+            try:
+                self.drive_high()
+            except AssertionError:
+                # Charging pins are typically flipped between input and output
+                # repeatedly; if another thread has already flipped us to
+                # output ignore the assertion-error resulting from attempting
+                # to drive the pin high
+                pass
+
+
+class MockTriggerPin(MockPin):
+    """
+    This derivative of :class:`MockPin` is intended to be used with another
+    :class:`MockPin` to emulate a distance sensor. Set :attr:`echo_pin` to the
+    corresponding pin instance. When this pin is driven high it will trigger
+    the echo pin to drive high for the echo time.
+    """
+    def __init__(self, number):
+        super(MockTriggerPin, self).__init__()
+        self.echo_pin = None
+        self.echo_time = 0.04 # longest echo time
+        self._echo_thread = None
+
+    def _set_state(self, value):
+        super(MockTriggerPin, self)._set_state(value)
+        if value:
+            if self._echo_thread:
+                self._echo_thread.join()
+            self._echo_thread = Thread(target=self._echo)
+            self._echo_thread.start()
+
+    def _echo(self):
+        sleep(0.001)
+        self.echo_pin.drive_high()
+        sleep(self.echo_time)
+        self.echo_pin.drive_low()
 
 
 class MockPWMPin(MockPin):