assertFailsWith<IllegalArgumentException> {
      Headers.Builder().add(": bar")
    }
    assertFailsWith<IllegalArgumentException> {
      Headers.Builder().add(" : bar")
    }
  }

  @Test fun addThrowsOnNoColon() {
    assertFailsWith<IllegalArgumentException> {
      Headers.Builder().add("foo bar")
    }
  }

  @Test fun addThrowsOnMultiColon() {
    assertFailsWith<IllegalArgumentException> {