IVGCVSW-1988: Refactor backend-specific unit tests

Change-Id: I8eca81d2e0780390eaa837c186ffe1c7d41fdebe
diff --git a/src/backends/reference/backend.cmake b/src/backends/reference/backend.cmake
index 95e72a4..5ae088a 100644
--- a/src/backends/reference/backend.cmake
+++ b/src/backends/reference/backend.cmake
@@ -5,3 +5,4 @@
 
 add_subdirectory(${PROJECT_SOURCE_DIR}/src/backends/reference)
 list(APPEND armnnLibraries armnnRefBackend armnnRefBackendWorkloads)
+list(APPEND armnnUnitTestLibraries armnnRefBackendUnitTests)