How to check a log/output in go test?

I have this function that logs the error in some cases:

    func readByte(...){
     ...
     if err != nil {
     fmt.Println("ERROR")
     log.Print("Couldn't read first byte")
     return
     }
     ...
    }

Now, in the test file, I want to check the output error from this function:

    c.Assert(OUTPUT, check.Matches, "teste")

How can I access the log? I tried to put a buffer but it didn't work. What is the right way to catch this log without change my readByte function code?