Merge branch 'add_unittest' into 'branch-0.3.1'

Add unittest

See merge request megasearch/milvus!187

Former-commit-id: a26ab4638fff2a70b085a5abb16ebaa5ee163178

cpp/unittest/index_wrapper/CMakeLists.txt

@@ -20,4 +20,6 @@ set(knowhere_libs
         )
 
 add_executable(knowhere_test knowhere_test.cpp ${knowhere_src} ${helper})
-target_link_libraries(knowhere_test ${knowhere_libs} ${unittest_libs})
\ No newline at end of file
+target_link_libraries(knowhere_test ${knowhere_libs} ${unittest_libs})
+
+install(TARGETS knowhere_test DESTINATION bin)
\ No newline at end of file