Add unit tests for FactoryBot::Linter

Add spec coverage for the Linter class which previously had no
corresponding unit test file. Tests cover valid/invalid factory
linting, error message formatting, FactoryError and
FactoryTraitError message formatting including verbose backtrace.

Author: hammadxcm

spec/factory_bot/linter_spec.rb

@@ -0,0 +1,81 @@
+describe FactoryBot::Linter do
+  describe "#lint!" do
+    it "does not raise when all factories are valid" do
+      define_class("User") { attr_accessor :name }
+      FactoryBot.define do
+        factory :linter_user, class: "User" do
+          name { "Test" }
+        end
+      end
+
+      factories = FactoryBot.factories.select { |f| f.name == :linter_user }
+      linter = described_class.new(factories, strategy: :build)
+
+      expect { linter.lint! }.not_to raise_error
+    end
+
+    it "raises InvalidFactoryError when a factory is invalid" do
+      define_class("LinterFailModel") {
+        def save!
+          raise "validation failed"
+        end
+      }
+      FactoryBot.define do
+        factory :linter_fail_model, class: "LinterFailModel"
+      end
+
+      factories = FactoryBot.factories.select { |f| f.name == :linter_fail_model }
+      linter = described_class.new(factories, strategy: :create)
+
+      expect { linter.lint! }.to raise_error(FactoryBot::InvalidFactoryError)
+    end
+
+    it "includes factory name in error message" do
+      define_class("LinterBadModel") {
+        def save!
+          raise "cannot save"
+        end
+      }
+      FactoryBot.define do
+        factory :linter_bad_model, class: "LinterBadModel"
+      end
+
+      factories = FactoryBot.factories.select { |f| f.name == :linter_bad_model }
+      linter = described_class.new(factories, strategy: :create)
+
+      expect { linter.lint! }.to raise_error(/linter_bad_model/)
+    end
+  end
+
+  describe described_class::FactoryError do
+    it "formats error message with factory name and error details" do
+      wrapped_error = RuntimeError.new("something went wrong")
+      factory = double("factory", name: :user)
+      error = described_class.new(wrapped_error, factory)
+
+      expect(error.message).to include("user")
+      expect(error.message).to include("something went wrong")
+      expect(error.message).to include("RuntimeError")
+    end
+
+    it "includes backtrace in verbose message" do
+      wrapped_error = RuntimeError.new("something went wrong")
+      wrapped_error.set_backtrace(["line1.rb:1", "line2.rb:2"])
+      factory = double("factory", name: :user)
+      error = described_class.new(wrapped_error, factory)
+
+      expect(error.verbose_message).to include("line1.rb:1")
+      expect(error.verbose_message).to include("line2.rb:2")
+    end
+  end
+
+  describe described_class::FactoryTraitError do
+    it "includes factory and trait name in location" do
+      wrapped_error = RuntimeError.new("trait error")
+      factory = double("factory", name: :user)
+      error = described_class.new(wrapped_error, factory, :admin)
+
+      expect(error.message).to include("user+admin")
+    end
+  end
+end