Linux下开箱即用的C++单元测试demo示例，private成员函数单元测试

# Customization Points The custom directory is an injection point for custom user configurations. ## Header `gtest.h` ### The following macros can be defined: * `GTEST_OS_STACK_TRACE_GETTER_` - The name of an implementation of `OsStackTraceGetterInterface`. * `GTEST_CUSTOM_TEMPDIR_FUNCTION_` - An override for `testing::TempDir()`. See `testing::TempDir` for semantics and signature. ## Header `gtest-port.h` The following macros can be defined: ### Flag related macros: * `GTEST_FLAG(flag_name)` * `GTEST_USE_OWN_FLAGFILE_FLAG_` - Define to 0 when the system provides its own flagfile flag parsing. * `GTEST_DECLARE_bool_(name)` * `GTEST_DECLARE_int32_(name)` * `GTEST_DECLARE_string_(name)` * `GTEST_DEFINE_bool_(name, default_val, doc)` * `GTEST_DEFINE_int32_(name, default_val, doc)` * `GTEST_DEFINE_string_(name, default_val, doc)` ### Logging: * `GTEST_LOG_(severity)` * `GTEST_CHECK_(condition)` * Functions `LogToStderr()` and `FlushInfoLog()` have to be provided too. ### Threading: * `GTEST_HAS_NOTIFICATION_` - Enabled if Notification is already provided. * `GTEST_HAS_MUTEX_AND_THREAD_LOCAL_` - Enabled if `Mutex` and `ThreadLocal` are already provided. Must also provide `GTEST_DECLARE_STATIC_MUTEX_(mutex)` and `GTEST_DEFINE_STATIC_MUTEX_(mutex)` * `GTEST_EXCLUSIVE_LOCK_REQUIRED_(locks)` * `GTEST_LOCK_EXCLUDED_(locks)` ### Underlying library support features * `GTEST_HAS_CXXABI_H_` ### Exporting API symbols: * `GTEST_API_` - Specifier for exported symbols. ## Header `gtest-printers.h` * See documentation at `gtest/gtest-printers.h` for details on how to define a custom printer.