Add unit tests for FactoryBot::Syntax::Default

Add spec coverage for the Syntax::Default module, DSL, and ModifyDSL
classes which previously had no corresponding unit test file. Tests
cover factory/sequence/trait registration, factory modification,
child factories, and DSL.run block evaluation.

Author: hammadxcm

spec/factory_bot/syntax/default_spec.rb

@@ -0,0 +1,92 @@
+describe FactoryBot::Syntax::Default do
+  describe "FactoryBot.define" do
+    it "registers a factory" do
+      define_class("SyntaxDefaultUser") { attr_accessor :name }
+
+      FactoryBot.define do
+        factory :syntax_default_user, class: "SyntaxDefaultUser" do
+          name { "Test" }
+        end
+      end
+
+      expect(FactoryBot::Internal.factory_by_name(:syntax_default_user)).to be_a FactoryBot::Factory
+    end
+
+    it "registers a sequence" do
+      FactoryBot.define do
+        sequence(:syntax_default_email) { |n| "user#{n}@example.com" }
+      end
+
+      expect(FactoryBot.generate(:syntax_default_email)).to match(/user\d+@example\.com/)
+    end
+
+    it "registers a global trait" do
+      FactoryBot.define do
+        trait :syntax_default_admin do
+        end
+      end
+
+      expect(FactoryBot::Internal.traits.find(:syntax_default_admin)).to be_a FactoryBot::Trait
+    end
+  end
+
+  describe "FactoryBot.modify" do
+    it "modifies an existing factory" do
+      define_class("SyntaxModifyUser") { attr_accessor :name }
+
+      FactoryBot.define do
+        factory :syntax_modify_user, class: "SyntaxModifyUser" do
+          name { "Original" }
+        end
+      end
+
+      FactoryBot.modify do
+        factory :syntax_modify_user do
+          name { "Modified" }
+        end
+      end
+
+      user = FactoryBot.build(:syntax_modify_user)
+      expect(user.name).to eq "Modified"
+    end
+  end
+
+  describe FactoryBot::Syntax::Default::DSL do
+    describe "#factory" do
+      it "handles child factories" do
+        define_class("SyntaxChildUser") { attr_accessor :name, :role }
+
+        FactoryBot.define do
+          factory :syntax_child_user, class: "SyntaxChildUser" do
+            name { "Test" }
+
+            factory :syntax_child_admin do
+              role { "admin" }
+            end
+          end
+        end
+
+        admin = FactoryBot.build(:syntax_child_admin)
+        expect(admin.name).to eq "Test"
+        expect(admin.role).to eq "admin"
+      end
+    end
+
+    describe ".run" do
+      it "evaluates the block in the context of a new DSL instance" do
+        define_class("SyntaxRunUser") { attr_accessor :name }
+
+        block = proc {
+          factory :syntax_run_user, class: "SyntaxRunUser" do
+            name { "from block" }
+          end
+        }
+
+        described_class.run(block)
+
+        user = FactoryBot.build(:syntax_run_user)
+        expect(user.name).to eq "from block"
+      end
+    end
+  end
+end