The framework in the testing package prints its output to os.Stdout. A caller might want to redirect this elsewhere, or alter it - e.g. to write to a file as well which another system might parse. This can be achieved by replacing os.Stdout, but this is overly difficult since it's a File (#13473 suggests this is known to be undesirable but can't change before v2), requiring e.g. os.Pipe and associated management + overhead. However, testing only needs an io.Writer rather than the full os.File type.

I propose that we add a new function to the testing package allowing a caller to set the stream that is output to, along the lines of:

// OutputStream sets the stream to which testing output is written.
// It must be called before any tests, benchmarks or fuzz suites are run, and should not be called while they are running.
// If not called, the default is os.Stdout
func OutputStream(w io.Writer) {
    outputStream = w
}

var outputStream = os.Stdout

I might be being a little defensive about not exposing the variable directly, but it feels like the function is a clearer documentation point and helps future-proof the interface a bit.