test: add read and write interface mocks

The pluggable sensor object receives a reader and writer
interface.  These are now mocked to enable some testing that
involves Pluggable Sensors.

Change-Id: If2d121ab47a2c044b0f3fd3465bfe45cf26c4f98
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/test/writeinterface_mock.hpp b/test/writeinterface_mock.hpp
new file mode 100644
index 0000000..4fab5fb
--- /dev/null
+++ b/test/writeinterface_mock.hpp
@@ -0,0 +1,14 @@
+#pragma once
+
+#include "interfaces.hpp"
+
+class WriteInterfaceMock : public WriteInterface
+{
+    public:
+        virtual ~WriteInterfaceMock() = default;
+
+        WriteInterfaceMock(int64_t min, int64_t max)
+            : WriteInterface(min, max) {}
+
+        MOCK_METHOD1(write, void(double));
+};