Adds validations for active model errors

Allows asserting that the correct validations were added to a model.
Streamline the testing process for validations and make it easier for developers to understand the purpose of each test case.

activesupport/CHANGELOG.md

@@ -1,2 +1,11 @@
+*   Adds `assert_error`, `assert_no_error`, `assert_valid` and `assert_not_valid` to ensure a model has the right validations
+    ```ruby
+    assert_error :name, :blank, :user
+    assert_no_error :name, :blank, :user
+    assert_valid :name, :blank, :user
+    assert_not_valid :name, :blank, :user
+    ```
+
+    *Daniela Velasquez*
 
 Please check [7-2-stable](https://github.com/rails/rails/blob/7-2-stable/activesupport/CHANGELOG.md) for previous changes.

activesupport/lib/active_support/testing/assertions.rb

@@ -261,6 +261,50 @@ def assert_no_changes(expression, message = nil, from: UNTRACKED, &block)
         retval
       end
 
+      # Assertion that an active model doesn't have an error on a field
+      #
+      # assert_no_error :name, :blank, :user
+      def assert_no_error(attribute, type, obj, msg = nil)
+        raise ArgumentError.new("#{obj.inspect} does not respond to #errors") unless obj.respond_to?(:errors)
+        msg = message(msg) {
+          data = [attribute, type]
+          "Expected %s to not be %s" % data
+        }
+        assert_empty obj.errors.where(attribute, type), msg
+      end
+
+      # Assertion that an active model has a specific error on a field
+      #
+      # assert_error :name, :blank, :user
+      def assert_error(attribute, type, obj, msg = nil)
+        raise ArgumentError.new("#{obj.inspect} does not respond to #errors") unless obj.respond_to?(:errors)
+        msg = message(msg) {
+          data = [attribute, type]
+          "Expected %s to be %s" % data
+        }
+        refute_empty obj.errors.where(attribute, type), msg
+      end
+
+      # Assertion that an active model's attribute is not valid after validation
+      #
+      # assert_not_valid :name, :blank, :user
+      def assert_not_valid(attribute, type, obj, msg = nil)
+        raise ArgumentError.new("#{obj.inspect} does not respond to #validate") unless obj.respond_to?(:validate)
+
+        obj.validate
+        assert_error(attribute, type, obj, msg)
+      end
+
+      # Assertion that an active model's attribute is valid after validation
+      #
+      # assert_valid :name, :blank, :user
+      def assert_valid(attribute, type, obj, msg = nil)
+        raise ArgumentError.new("#{obj.inspect} does not respond to #validate") unless obj.respond_to?(:validate)
+
+        obj.validate
+        assert_no_error(attribute, type, obj, msg)
+      end
+
       private
         def _assert_nothing_raised_or_warn(assertion, &block)
           assert_nothing_raised(&block)

activesupport/test/active_model_test.rb

@@ -0,0 +1,103 @@
+# frozen_string_literal: true
+
+require_relative "abstract_unit"
+require "active_model"
+
+class ActiveModelTest < ActiveSupport::TestCase
+  def setup
+    @active_model = Class.new do
+      include ActiveModel::Model
+      include ActiveModel::Attributes
+
+      attribute :name, :string
+      attribute :last_name, :string
+      validates :name, :last_name, presence: true
+    end.new
+  end
+
+  test "#assert_no_error asserts active model does not have an error on a field" do
+    @active_model.name = "name"
+    @active_model.validate
+
+    assert_no_error :name, :blank, @active_model
+  end
+
+  test "#assert_no_error raises ArgumentError with a non-active record" do
+    error = assert_raises(ArgumentError) do
+        assert_no_error :name, :blank, Object.new
+      end
+
+    assert_includes error.message, "does not respond to #errors"
+  end
+
+  test "#assert_no_error raises a Minitest::Assertion when validation fails" do
+    @active_model.validate
+    error = assert_raises(Minitest::Assertion) do
+      assert_no_error :name, :blank,  @active_model
+    end
+    assert_includes error.message, "Expected name to not be blank"
+  end
+
+  test "#assert_error asserts active model has an error on a field" do
+    @active_model.validate
+    assert_error :name, :blank, @active_model
+  end
+
+  test "#assert_error raises ArgumentError with a non-active record" do
+    error = assert_raises(ArgumentError) do
+      assert_error :name, :blank, Object.new
+    end
+
+    assert_includes error.message, "does not respond to #errors"
+  end
+
+  test "#assert_error raises a Minitest::Assertion when validation fails" do
+    @active_model.name = "h"
+    @active_model.validate
+    error = assert_raises(Minitest::Assertion) do
+      assert_error :name, :blank,  @active_model
+    end
+    assert_includes error.message, "Expected name to be blank"
+  end
+
+  test "#assert_not_valid asserts active model has error on a field after validation" do
+    assert_not_valid :name, :blank, @active_model
+  end
+
+  test "#assert_not_valid raises ArgumentError with message about the object nor responding to validate" do
+    error = assert_raises(ArgumentError) do
+      assert_not_valid :name, :blank, Object.new
+    end
+
+    assert_includes error.message, "does not respond to #validate"
+  end
+
+  test "#assert_not_valid raises a Minitest::Assertion when validation fails" do
+    @active_model.name = "Hi"
+    error = assert_raises(Minitest::Assertion) do
+      assert_not_valid :name, :blank,  @active_model
+    end
+    assert_includes error.message, "Expected name to be blank"
+  end
+
+  test "#assert_valid asserts active model does not have an error on a field after validation" do
+    @active_model.name = "name"
+
+    assert_valid :name, :blank, @active_model
+  end
+
+  test "#assert_valid raises ArgumentError with message about the object nor responding to validate" do
+    error = assert_raises(ArgumentError) do
+      assert_valid :name, :blank, Object.new
+    end
+
+    assert_includes error.message, "does not respond to #validate"
+  end
+
+  test "#assert_valid raises a Minitest::Assertion when validation fails" do
+    error = assert_raises(Minitest::Assertion) do
+      assert_valid :name, :blank,  @active_model
+    end
+    assert_includes error.message, "Expected name to not be blank"
+  end
+end

railties/CHANGELOG.md

@@ -1,6 +1,6 @@
 *   Use Kamal for deployment by default, which includes generating a Rails-specific config/deploy.yml.
     This can be skipped using --skip-kamal. See more: https://kamal-deploy.org/
 
-    *DHH* 
+    *DHH*
 
 Please check [7-2-stable](https://github.com/rails/rails/blob/7-2-stable/railties/CHANGELOG.md) for previous changes.