go test: mock multi contract interface: embed self

[AmitKumarDas]

• refer: https://github.com/mvdan/sh/blob/master/expand/expand_test.go

type mockFileInfo struct {
  name string
  typ fs.FileMode

  // Stub out everything but Name() & Type()
  fs.DirEntry // nice: does this lazy stuff really work
}

var _ fs.DirEntry = (*mockFileInfo)(nil)

func (fi *mockFileInfo) Name() string { return [fi.name](http://fi.name/) }
func (fi *mockFileInfo) Type() fs.FileMode { return fi.typ }