a.rb

NewFamilyForm = Dry::Validation.Form do
  required(:email).filled(format?: /.@.+[.][a-z]{1}/i)

  # I've tried various things here, all to no effect
  # required(:adult).filled(:array?, min_size?: 1)
  required(:adult).value(:array?, :filled?, min_size?: 1)
  required(:adult).each do
    none? | (str? & min_size?(1))
  end

  required(:child).each do
    none? | (str? & min_size?(1))
  end
end

class NewFamilyFormTest < Minitest::Test
  def test_requires_email
    result = NewFamilyForm.call({})
    assert_equal ["is missing"], result.errors[:email]
    assert_equal({}, result.output)
  end

  def test_requires_adult_key
    result = NewFamilyForm.call({})
    assert_equal ["is missing"], result.errors[:adult]
    assert_equal({}, result.output)
  end

  # This test FAILS, what must I change to make it green?
  def test_requires_at_least_one_adult
    result = NewFamilyForm.call("adult" => [])
    assert_equal 1, result.errors[:adult], result.errors.inspect
    assert_equal({adult: []}, result.output)
  end

  # I can live with this
  def test_ignores_empty_names
    result = NewFamilyForm.call("adult" => ["francois", ""])
    assert_nil result.errors[:adult]
    assert_equal({adult: ["francois", nil]}, result.output)
  end
end

a.txt

  1) Failure:
NewFamilyFormTest#test_requires_at_least_one_adult [test/test_new_family_form.rb:19]:
{:email=>["is missing"], :child=>["is missing"]}.
Expected: 1
  Actual: nil

z-invalid.txt

{}
#=> errors: missing the email field, missing the adult field

{"email" => "",
 "adult" => [],
 "child" => []}
#=> errors: email doesn't look like an email address, must have at least one adult

{"email" => "francois",
 "adult" => ["", " ", "\t"],
 "child" => []}
#=> errors: email doesn't look like an email address, must have at least one adult

z-valid.txt

# NOTE: I can live with nil values, because I can compact before using


{"email" => "francois@teksol.info",
 "adult" => ["francois", "\t"],
 "child" => ["      ", "", nil]}
#=> {email: "francois@teksol.info", adult: ["francois"], child: []}

{"email" => "francois@teksol.info",
 "adult" => [" ", "francois"],
 "child" => ["harry", "ron", "hermione", "ginny", "fred", "george", " "]}
#=> {email: "francois@teksol.info", adult: ["francois"], child: %w(harry ron hermione ginny fred george)}