How are embedded systems designed to make troubleshooting easier ?

By the help of generic monitor that you have in the code, which can be invoked only 

Certain mode ( referred as slots, ), this piece of code sits inside the box and let the tester know what is happening within the box. Normally these piece of code is 100% dormant.

The software is shipped finally with the box, to be used in flight. Also providing software hooks.

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