Added getDeviceCount and tests.
diff --git a/net/core/trivial/src/main/java/org/onlab/onos/net/trivial/impl/SimpleDeviceStore.java b/net/core/trivial/src/main/java/org/onlab/onos/net/trivial/impl/SimpleDeviceStore.java
index a49384b..dd63469 100644
--- a/net/core/trivial/src/main/java/org/onlab/onos/net/trivial/impl/SimpleDeviceStore.java
+++ b/net/core/trivial/src/main/java/org/onlab/onos/net/trivial/impl/SimpleDeviceStore.java
@@ -28,7 +28,8 @@
 import static org.onlab.onos.net.device.DeviceEvent.Type.*;
 
 /**
- * Manages inventory of infrastructure devices.
+ * Manages inventory of infrastructure devices using trivial in-memory
+ * implementation.
  */
 class SimpleDeviceStore {
 
@@ -40,6 +41,15 @@
     private final Map<DeviceId, Map<PortNumber, Port>> devicePorts = new HashMap<>();
 
     /**
+     * Returns the number of devices known to the system.
+     *
+     * @return number of devices
+     */
+    public int getDeviceCount() {
+        return devices.size();
+    }
+
+    /**
      * Returns an iterable collection of all devices known to the system.
      *
      * @return device collection
@@ -301,5 +311,4 @@
                     new DeviceEvent(DEVICE_REMOVED, device, null);
         }
     }
-
 }