service/test: Fix a wrong judgment about err.
service/test: Fix a wrong judgment about err.

Should judge `state.Err` instead of `err`.

go-delve/delve,go-delve/delve,aarzilli/delve,go-delve/delve,go-delve/delve,aarzilli/delve,derekparker/delve,derekparker/delve,aarzilli/delve,go-delve/delve,aarzilli/delve,derekparker/delve