}
	if err != nil && err.Error() != "550 "+wantMsg {
		t.Errorf("ReadResponse: error=%q, want %q", err.Error(), "550 "+wantMsg)
	}
}

func TestCommonHeaders(t *testing.T) {
	commonHeaderOnce.Do(initCommonHeader)
	for h := range commonHeader {
		if h != CanonicalMIMEHeaderKey(h) {
			t.Errorf("Non-canonical header %q in commonHeader", h)
		}
	}
	b := []byte("content-Length")
	want := "Content-Length"

		if upper && 'a' <= c && c <= 'z' {
			c -= toLower
		} else if !upper && 'A' <= c && c <= 'Z' {
			c += toLower
		}
		a[i] = c
		upper = c == '-' // for next time
	}
	commonHeaderOnce.Do(initCommonHeader)
	// The compiler recognizes m[string(byteSlice)] as a special
	// case, so a copy of a's bytes into a new string does not
	// happen in this map lookup:
	if v := commonHeader[string(a)]; v != "" {
		return v, true