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hardEmbedded Systems Engineer interview question

How do you build a strong automated testing strategy for embedded firmware?

What the interviewer wants to hear

  • Separate hardware-dependent code behind abstractions
  • Unit tests on the host with mocks and frameworks such as Unity or GoogleTest
  • Static analysis and MISRA checks
  • Hardware-in-the-loop tests on real boards in CI
  • Simulation or emulation such as QEMU or Renode
  • Fault injection and long-run soak tests

Model answer

The key is design for testability. I keep business logic, like control algorithms, protocol parsers and state machines, separate from hardware access, which sits behind a thin hardware abstraction layer. Then most code can be unit tested on a PC with Unity, Ceedling or GoogleTest, using mocks for the HAL, and it runs in seconds in CI with sanitisers that catch undefined behaviour. I add static analysis, such as cppcheck, clang-tidy or a MISRA checker, and compiler warnings as errors. For integration, I use emulators like Renode or QEMU to run the real firmware binary with simulated peripherals. Then hardware-in-the-loop: real boards connected to a CI runner, with a programmer, power control and test equipment, run automated tests on every merge, for example flashing, booting, exercising sensors and checking UART output. Finally, fault injection, like power cuts during flash writes, and multi-day soak tests catch leaks and rare timing issues.

Can you answer it under time pressure?

Take a timed hard round and get scored on every answer.

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