Published fragment Stubbing degenerate network conditions in Go with DialFunc and net.Conn, on using DialFunc to return a minimal stub for net.Conn that can simulate hard-to-reproduce conditions like an error on Close.

type connStub struct {
    net.Conn

    closeFunc func() error
}

func newConnStub(conn net.Conn) *connStub {
    return &connStub{
        Conn: conn,

        closeFunc: conn.Close,
    }
}

func (c *connStub) Close() error {
    return c.closeFunc()
}