A table driven test, for each of the cases in the code, would be useful.

Actually, this test is not very useful. It would be better to make an Executor/Task test where you have a list of files including characters which should be escaped, then run the Task, then check the files are handled correctly. You might even find that such a test exists.

Such a test would cover the entire processing chain (in case it gets broken somewhere else too).

Something like this would be better:

var pathReplacer = strings.NewReplacer(
	" ", `\ `,
	"&", `\&`,
	"(", `\(`,
	")", `\)`,
	"'", `\'`,
)

func escape(s string) string {
	s = filepath.ToSlash(s)
	return pathReplacer.Replace(s)
}

But I also wonder if there are other characters which need escaping?