feat: Add validating qualifier to enum matcher

On this commit we add a new qualifier to the `define_enum_for` matcher
called `validating`. This qualifier is used to test if the enum is being
validated or not.

```ruby
class Issue < ActiveRecord::Base
  enum status: [:open, :closed], validate: true
end

RSpec.describe Issue, type: :model do
  it do
    should define_enum_for(:status).
      validating
  end
end
```

lib/shoulda/matchers/active_record/define_enum_for_matcher.rb

@@ -212,6 +212,47 @@ module ActiveRecord
       #         with_default(:closed)
       #     end
       #
+      # ##### validating
+      #
+      # Use `validating` to test that the enum is being validated.
+      # Can take a boolean value and an allowing_nil keyword argument:
+      #
+      #     class Issue < ActiveRecord::Base
+      #       enum status: [:open, :closed], validate: true
+      #     end
+      #
+      #     # RSpec
+      #     RSpec.describe Issue, type: :model do
+      #       it do
+      #         should define_enum_for(:status).
+      #           validating
+      #       end
+      #     end
+      #
+      #     # Minitest (Shoulda)
+      #     class ProcessTest < ActiveSupport::TestCase
+      #       should define_enum_for(:status).
+      #         validating
+      #     end
+      #
+      #     class Issue < ActiveRecord::Base
+      #       enum status: [:open, :closed], validate: { allow_nil: true }
+      #     end
+      #
+      #     # RSpec
+      #     RSpec.describe Issue, type: :model do
+      #       it do
+      #         should define_enum_for(:status).
+      #           validating(allowing_nil: true)
+      #       end
+      #     end
+      #
+      #     # Minitest (Shoulda)
+      #     class ProcessTest < ActiveSupport::TestCase
+      #       should define_enum_for(:status).
+      #         validating(allowing_nil: true)
+      #     end
+      #
       # @return [DefineEnumForMatcher]
       #
       def define_enum_for(attribute_name)
@@ -247,6 +288,12 @@ def description
           description
         end
 
+        def validating(value = true, allowing_nil: false)
+          options[:validating] = value
+          options[:allowing_nil] = allowing_nil
+          self
+        end
+
         def with_values(expected_enum_values)
           options[:expected_enum_values] = expected_enum_values
           self
@@ -285,7 +332,8 @@ def matches?(subject)
             column_type_matches? &&
             enum_value_methods_exist? &&
             scope_presence_matches? &&
-            default_value_matches?
+            default_value_matches? &&
+            validating_matches?
         end
 
         def failure_message
@@ -308,6 +356,30 @@ def failure_message_when_negated
 
         private
 
+        def validating_matches?
+          return true if options[:validating].nil?
+
+          validator = find_enum_validator
+
+          if expected_validating? == !!validator
+            if validator&.options&.dig(:allow_nil).present? == expected_allowing_nil?
+              true
+            else
+              @failure_message_continuation =
+                "However, #{attribute_name.inspect} is allowing nil values"
+              false
+            end
+          else
+            @failure_message_continuation =
+              if expected_validating?
+                "However, #{attribute_name.inspect} is not being validated"
+              else
+                "However, #{attribute_name.inspect} is being validated"
+              end
+            false
+          end
+        end
+
         attr_reader :attribute_name, :options, :record,
           :failure_message_continuation
 
@@ -328,6 +400,16 @@ def expectation # rubocop:disable Metrics/MethodLength
               expectation << Shoulda::Matchers::Util.inspect_value(expected_default_value)
             end
 
+            if expected_validating?
+              expectation << ', and being validated '
+              expectation <<
+                if expected_allowing_nil?
+                  'allowing nil values'
+                else
+                  'not allowing nil values'
+                end
+            end
+
             if expected_prefix
               expectation <<
                 if expected_suffix
@@ -602,6 +684,22 @@ def expected_suffix
           end
         end
 
+        def expected_validating?
+          options[:validating].present?
+        end
+
+        def expected_allowing_nil?
+          options[:allowing_nil].present?
+        end
+
+        def find_enum_validator
+          record.class.validators.detect do |validator|
+            validator.kind == :inclusion &&
+              validator.attributes.include?(attribute_name.to_s) &&
+              validator.options[:in] == expected_enum_values
+          end
+        end
+
         def exclude_scopes?
           !options[:scopes]
         end

spec/unit/shoulda/matchers/active_record/define_enum_for_matcher_spec.rb

@@ -905,6 +905,217 @@ def self.statuses
     end
   end
 
+  if rails_version >= 7.1
+    describe 'qualified with #validating' do
+      context 'if enum is being validated' do
+        context 'but validating qualifier is not used' do
+          it 'matches' do
+            record = build_record_with_array_values(attribute_name: :attr, default: 'published', validate: true)
+
+            matcher = lambda do
+              define_enum_for(:attr).with_values(['published', 'unpublished', 'draft'])
+            end
+
+            message = format_message(<<-MESSAGE)
+              Expected Example not to define :attr as an enum backed by an integer,
+              mapping ‹"published"› to ‹0›, ‹"unpublished"› to ‹1›, and ‹"draft"›
+              to ‹2›, but it did.
+            MESSAGE
+
+            expect(&matcher).to match_against(record).or_fail_with(message)
+          end
+        end
+
+        context 'and validating qualifier is used as false' do
+          it 'rejects with an appropriate failure message' do
+            record = build_record_with_array_values(attribute_name: :attr, default: 'published', validate: true)
+
+            assertion = lambda do
+              expect(record).
+                to define_enum_for(:attr).
+                with_values(['published', 'unpublished', 'draft']).
+                validating(false)
+            end
+
+            message = format_message(<<-MESSAGE)
+              Expected Example to define :attr as an enum backed by an integer,
+              mapping ‹"published"› to ‹0›, ‹"unpublished"› to ‹1›, and ‹"draft"›
+              to ‹2›. However, :attr is being validated.
+            MESSAGE
+
+            expect(&assertion).to fail_with_message(message)
+          end
+        end
+
+        context 'and validating qualifier is used' do
+          it 'matches' do
+            record = build_record_with_array_values(attribute_name: :attr, validate: true)
+
+            matcher = lambda do
+              define_enum_for(:attr).
+                with_values(['published', 'unpublished', 'draft']).
+                validating
+            end
+
+            message = format_message(<<-MESSAGE)
+              Expected Example not to define :attr as an enum backed by an integer,
+              mapping ‹"published"› to ‹0›, ‹"unpublished"› to ‹1›, and ‹"draft"›
+              to ‹2›, and being validated not allowing nil values, but it did.
+            MESSAGE
+
+            expect(&matcher).to match_against(record).or_fail_with(message)
+          end
+        end
+
+        context 'using allow_nil' do
+          context 'when allowing nil on qualifier' do
+            it 'matches' do
+              record = build_record_with_array_values(attribute_name: :attr, validate: { allow_nil: true })
+
+              matcher = lambda do
+                define_enum_for(:attr).
+                  with_values(['published', 'unpublished', 'draft']).
+                  validating(allowing_nil: true)
+              end
+
+              message = format_message(<<-MESSAGE)
+                Expected Example not to define :attr as an enum backed by an integer,
+                mapping ‹"published"› to ‹0›, ‹"unpublished"› to ‹1›, and ‹"draft"›
+                to ‹2›, and being validated allowing nil values, but it did.
+              MESSAGE
+
+              expect(&matcher).to match_against(record).or_fail_with(message)
+            end
+          end
+
+          context 'when not allowing nil on qualifier' do
+            it 'rejects with an appropriate failure message' do
+              record = build_record_with_array_values(attribute_name: :attr, validate: { allow_nil: true })
+
+              assertion = lambda do
+                expect(record).
+                  to define_enum_for(:attr).
+                  with_values(['published', 'unpublished', 'draft']).
+                  validating
+              end
+
+              message = format_message(<<-MESSAGE)
+                Expected Example to define :attr as an enum backed by an integer,
+                mapping ‹"published"› to ‹0›, ‹"unpublished"› to ‹1›, and ‹"draft"›
+                to ‹2›, and being validated not allowing nil values. However, :attr is
+                allowing nil values.
+              MESSAGE
+
+              expect(&assertion).to fail_with_message(message)
+            end
+          end
+        end
+      end
+
+      context 'when not allowing nil values' do
+        it 'matches if qualifier does not allow' do
+          record = build_record_with_array_values(attribute_name: :attr, validate: { allow_nil: false })
+
+          matcher = lambda do
+            define_enum_for(:attr).
+              with_values(['published', 'unpublished', 'draft']).
+              validating(allowing_nil: false)
+          end
+
+          message = format_message(<<-MESSAGE)
+            Expected Example not to define :attr as an enum backed by an integer,
+            mapping ‹"published"› to ‹0›, ‹"unpublished"› to ‹1›, and ‹"draft"›
+            to ‹2›, and being validated not allowing nil values, but it did.
+          MESSAGE
+
+          expect(&matcher).to match_against(record).or_fail_with(message)
+        end
+
+        it 'rejects with an appropriate failure message if qualifier allows' do
+          record = build_record_with_array_values(attribute_name: :attr, validate: { allow_nil: false })
+
+          assertion = lambda do
+            expect(record).
+              to define_enum_for(:attr).
+              with_values(['published', 'unpublished', 'draft']).
+              validating(allowing_nil: true)
+          end
+
+          message = format_message(<<-MESSAGE)
+            Expected Example to define :attr as an enum backed by an integer,
+            mapping ‹"published"› to ‹0›, ‹"unpublished"› to ‹1›, and ‹"draft"›
+            to ‹2›, and being validated allowing nil values. However, :attr is allowing
+            nil values.
+          MESSAGE
+
+          expect(&assertion).to fail_with_message(message)
+        end
+      end
+
+      context 'if enum is not being validated' do
+        context 'but validating qualifier is used' do
+          it 'rejects with an appropriate failure message' do
+            record = build_record_with_array_values(attribute_name: :attr, default: 'published')
+
+            assertion = lambda do
+              expect(record).
+                to define_enum_for(:attr).
+                with_values(['published', 'unpublished', 'draft']).
+                validating
+            end
+
+            message = format_message(<<-MESSAGE)
+              Expected Example to define :attr as an enum backed by an integer,
+              mapping ‹"published"› to ‹0›, ‹"unpublished"› to ‹1›, and ‹"draft"›
+              to ‹2›, and being validated not allowing nil values. However, :attr
+              is not being validated.
+            MESSAGE
+
+            expect(&assertion).to fail_with_message(message)
+          end
+        end
+
+        context 'and validating qualifier is used as false' do
+          it 'matches' do
+            record = build_record_with_array_values(attribute_name: :attr, default: 'published')
+
+            matcher = lambda do
+              define_enum_for(:attr).
+                with_values(['published', 'unpublished', 'draft']).
+                validating(false)
+            end
+
+            message = format_message(<<-MESSAGE)
+              Expected Example not to define :attr as an enum backed by an integer,
+              mapping ‹"published"› to ‹0›, ‹"unpublished"› to ‹1›, and ‹"draft"›
+              to ‹2›, but it did.
+            MESSAGE
+
+            expect(&matcher).to match_against(record).or_fail_with(message)
+          end
+        end
+
+        context 'and validating qualifier is not used' do
+          it 'matches' do
+            record = build_record_with_array_values(attribute_name: :attr, default: 'published')
+
+            matcher = lambda do
+              define_enum_for(:attr).with_values(['published', 'unpublished', 'draft'])
+            end
+
+            message = format_message(<<-MESSAGE)
+              Expected Example not to define :attr as an enum backed by an integer,
+              mapping ‹"published"› to ‹0›, ‹"unpublished"› to ‹1›, and ‹"draft"›
+              to ‹2›, but it did.
+            MESSAGE
+
+            expect(&matcher).to match_against(record).or_fail_with(message)
+          end
+        end
+      end
+    end
+  end
+
   if rails_version =~ '~> 6.0'
     context 'qualified with #without_scopes' do
       context 'if scopes are set to false on the enum but without_scopes is not used' do
@@ -986,7 +1197,8 @@ def build_record_with_array_values(
     suffix: false,
     attribute_alias: nil,
     scopes: true,
-    default: nil
+    default: nil,
+    validate: false
   )
     build_record_with_enum_attribute(
       model_name: model_name,
@@ -998,6 +1210,7 @@ def build_record_with_array_values(
       attribute_alias: attribute_alias,
       scopes: scopes,
       default: default,
+      validate: validate,
     )
   end
 
@@ -1030,7 +1243,8 @@ def build_record_with_enum_attribute(
     scopes: true,
     prefix: false,
     suffix: false,
-    default: nil
+    default: nil,
+    validate: false
   )
     enum_name = attribute_alias || attribute_name
     model = define_model(
@@ -1048,7 +1262,7 @@ def build_record_with_enum_attribute(
     }
 
     if rails_version >= 7.0
-      model.enum(enum_name, values, prefix: prefix, suffix: suffix, default: default)
+      model.enum(enum_name, values, prefix: prefix, suffix: suffix, validate: validate, default: default)
     else
       params.merge!(_scopes: scopes)
       model.enum(params)