I believe you misunderstood. The OP wants to override unlink so he can test how the script handles errors from unlink. He's not asking how to check if unlink returned an error.

We do something similar at my workplace. In our test environment, we hook into the OS to control the exit codes returned by the disk reading function, the analog input reading function, the analog output writing function, etc. to ensure that our software properly handles those errors.

In reply to Re^2: Unit testing built-in functions by ikegami
in thread Unit testing built-in functions by aijin

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