To elaborate, this is a direct result of the method used to check whether the imaginary component is negligible compared to the real component, namely the expression isapprox(x - im*img, x) evaluates to false when the real part is exactly zero

function safe_real(x)
    img = imag(x)
    if !(iszero(img) || isapprox(x - im*img, x))
        error("Can not convert number $x to real due to its large imaginary part.")
    end
    return real(x)
end

A possible solution is to give expect a throw option, whereas for expect(...; nothrow=True), it will just use real to obtain the real part when the user is sure about the result. I don't know what was the original motivation for adding this, in what case @GiggleLiu is expecting expect to throw an error and terminate the program?

Thanks for the issue, just submitted a PR to fix the issue.