diff --git a/spec/sse/connection_proxy_spec.rb b/spec/sse/connection_proxy_spec.rb
new file mode 100644
index 00000000..c6efbb7b
--- /dev/null
+++ b/spec/sse/connection_proxy_spec.rb
@@ -0,0 +1,118 @@
+# frozen_string_literal: true
+
+RSpec.describe Rage::SSE::ConnectionProxy do
+  let(:connection) { MockConnection.new }
+  let(:proxy) { described_class.new(connection) }
+
+  # Minimal mock that mirrors Iodine's connection interface
+  class MockConnection
+    attr_reader :messages
+
+    def initialize(open: true)
+      @messages = []
+      @open = open
+    end
+
+    def write(data)
+      @messages << data
+      true
+    end
+
+    def close
+      @open = false
+      true
+    end
+
+    def open?
+      @open
+    end
+  end
+
+  describe "#write" do
+    it "writes data to the connection" do
+      proxy.write("data: hello\n\n")
+      expect(connection.messages).to eq(["data: hello\n\n"])
+    end
+
+    it "converts data to string" do
+      proxy.write(42)
+      expect(connection.messages).to eq(["42"])
+    end
+
+    it "writes multiple times" do
+      proxy.write("first")
+      proxy.write("second")
+      expect(connection.messages).to eq(["first", "second"])
+    end
+
+    it "raises IOError when connection is closed" do
+      connection.close
+      expect { proxy.write("data") }.to raise_error(IOError, "closed stream")
+    end
+  end
+
+  describe "#<<" do
+    it "writes data to the connection" do
+      proxy << "data: hello\n\n"
+      expect(connection.messages).to eq(["data: hello\n\n"])
+    end
+
+    it "converts data to string" do
+      proxy << 42
+      expect(connection.messages).to eq(["42"])
+    end
+
+    it "raises IOError when connection is closed" do
+      connection.close
+      expect { proxy << "data" }.to raise_error(IOError, "closed stream")
+    end
+  end
+
+  describe "#close" do
+    it "closes the connection" do
+      proxy.close
+      expect(proxy.closed?).to be true
+    end
+  end
+
+  describe "#close_write" do
+    it "closes the connection" do
+      proxy.close_write
+      expect(proxy.closed?).to be true
+    end
+  end
+
+  describe "#closed?" do
+    it "returns false when connection is open" do
+      expect(proxy.closed?).to be false
+    end
+
+    it "returns true when connection is closed" do
+      connection.close
+      expect(proxy.closed?).to be true
+    end
+  end
+
+  describe "#flush" do
+    it "does not raise when connection is open" do
+      expect { proxy.flush }.not_to raise_error
+    end
+
+    it "raises IOError when connection is closed" do
+      connection.close
+      expect { proxy.flush }.to raise_error(IOError, "closed stream")
+    end
+  end
+
+  describe "#read" do
+    it "is a no-op" do
+      expect(proxy.read).to be_nil
+    end
+  end
+
+  describe "#close_read" do
+    it "is a no-op" do
+      expect(proxy.close_read).to be_nil
+    end
+  end
+end