You can add a new c++ test using googletest (example).
To hook the test up using Bazel, add the following to the BUILD-file, adding in any extra dependencies that might be required for the test.
cc_test(
name = "example_test",
srcs = ["example_test.cpp"],
copts = ["-Iexternal/gtest/include"],
deps = [
"@googletest//:gtest_main",
]
)