test: Make sure mocks compile

This makes sure we don't accidentally change our interface without
updating the mock.

Change-Id: I50c6827e637167f1223d91f724b99ef8a24b107f
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/test/mocks.cpp b/test/mocks.cpp
new file mode 100644
index 0000000..2bc1f61
--- /dev/null
+++ b/test/mocks.cpp
@@ -0,0 +1,14 @@
+#include <gpioplus/test/handle.hpp>
+
+namespace gpioplus
+{
+namespace
+{
+
+TEST(Mocks, Compile)
+{
+    test::HandleMock handle;
+}
+
+} // namespace
+} // namespace gpioplus