[RF] Replace `assert` in test_HWM.cxx with `EXPECT_EQ`
[RF] Replace `assert` in test_HWM.cxx with `EXPECT_EQ`

This changes was motivated by an unused variable warning when building
not in debug mode.

olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root