Removes default visibility in debug mode and updates unit tests for alt_rsmi impl (#2091)

* Update unit tests for alt_rsmi impl

- Create distinct test executable for alt_rsmi testing
- Updated alt_rsmi tests to use public methods
- Compiles alt_rsmi.cc with ARSMI_TEST_BUILD
- Enables external linkage of internal variables
- Only for AltRsmiTests.cpp that manipulates internals
- Clean separation for test behavior

* Address review comments

* restore hidden symbol visibility

test/CMakeLists.txt

@@ -236,6 +236,25 @@ if(BUILD_TESTS)
       list(APPEND RCCL_TEST_EXECUTABLES rccl-UnitTestsMPI)
 
     endif()
+
+    # rccl-UnitTestsAltRsmi: Uses TEST BUILD alt_rsmi.cc (ARSMI_TEST_BUILD)
+    # This separate executable compiles alt_rsmi.cc with ARSMI_TEST_BUILD,
+    # enabling external linkage of internal variables so that
+    # tests can access and manipulate them for testing.
+    list(APPEND RCCL_TEST_EXECUTABLES rccl-UnitTestsAltRsmi)
+
+    set(TEST_ALTRSMI_SOURCE_FILES
+      AltRsmiTests.cpp
+      ../src/misc/alt_rsmi.cc
+      common/main_fixtures.cpp
+      common/EnvVars.cpp
+      common/ProcessIsolatedTestRunner.cpp
+    )
+
+    add_executable(rccl-UnitTestsAltRsmi ${TEST_ALTRSMI_SOURCE_FILES})
+
+    # Define ARSMI_TEST_BUILD specifically for rccl-UnitTestsAltRsmi
+    target_compile_definitions(rccl-UnitTestsAltRsmi PRIVATE ARSMI_TEST_BUILD)
   endif()
 
   foreach(test_executable IN LISTS RCCL_TEST_EXECUTABLES)