domain: String,
    registrablePart: String?,
  ) {
    val canonicalDomain = domain.toCanonicalHost() ?: return
    val result = publicSuffixDatabase.getEffectiveTldPlusOne(canonicalDomain)
    if (registrablePart == null) {
      assertThat(result).isNull()
    } else {
      assertThat(result).isEqualTo(registrablePart.toCanonicalHost())
    }
  }