> configure the ethernet
This is very vague. If you want to set up LwIP, there are examples within CubeMX which use ethernet. Use one of those for reference. The code will be different if you're on a custom board.
https://github.com/STMicroelectronics/STM32CubeF4/tree/master/Projects/STM324x9I_EVAL/Applications/LwIP
> how can I test the working.
This is also very vague. Typically you determine what you want to work and design tests to ensure those things function properly.
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