Fix ViolationError#object_class being always nil

lib/async/safe/violation_error.rb

@@ -16,6 +16,7 @@ class ViolationError < StandardError
 			# @parameter current [Fiber] The fiber that attempted to access the object.
 			def initialize(message = nil, target:, method:, owner:, current:)
 				@target = target
+				@object_class = target.class
 				@method = method
 				@owner = owner
 				@current = current

test/async/safe/violation_error.rb

@@ -6,20 +6,35 @@
 require "async/safe"
 
 describe Async::Safe::ViolationError do
-	it "can be serialized to JSON" do
-		owner_fiber = Fiber.current
-		current_fiber = Fiber.new{}.tap(&:resume)
-		
-		error = Async::Safe::ViolationError.new(
+	let(:owner_fiber) {Fiber.current}
+	let(:current_fiber) {Fiber.new{}.tap(&:resume)}
+
+	let(:error) do
+		Async::Safe::ViolationError.new(
 			target: "test_object",
 			method: :test_method,
 			owner: owner_fiber,
 			current: current_fiber
 		)
-
+	end
+
+	it "exposes object_class as the class of the target" do
+		expect(error.object_class).to be == String
+	end
+
+	it "exposes the method name" do
+		expect(error.method).to be == :test_method
+	end
+
+	it "exposes owner and current fibers" do
+		expect(error.owner).to be == owner_fiber
+		expect(error.current).to be == current_fiber
+	end
+
+	it "serializes object_class correctly in as_json" do
 		json = error.as_json
 
-		expect(json[:object_class]).to be == nil  # Not set
+		expect(json[:object_class]).to be == String
 		expect(json[:method]).to be == :test_method
 		expect(json[:owner]).to be_a(Hash)
 		expect(json[:current]).to be_a(Hash)