diff --git a/test/utils_test.rb b/test/utils_test.rb
new file mode 100644
index 0000000000..aadb6f85f2
--- /dev/null
+++ b/test/utils_test.rb
@@ -0,0 +1,34 @@
+# typed: true
+# frozen_string_literal: true
+
+require "test_helper"
+
+class UtilsTest < Minitest::Test
+  def test_convert_to_byte_offset_position_with_utf8
+    source = "hello"
+    assert_equal 2, RubyLsp.convert_to_byte_offset_position(source, 2, Encoding::UTF_8)
+    assert_equal 5, RubyLsp.convert_to_byte_offset_position(source, 5, Encoding::UTF_8)
+
+    # test multibyte characters
+    source = "こんにちは"
+    assert_equal 9, RubyLsp.convert_to_byte_offset_position(source, 3, Encoding::UTF_8)
+    assert_equal 15, RubyLsp.convert_to_byte_offset_position(source, 5, Encoding::UTF_8)
+  end
+
+  def test_convert_to_byte_offset_position_with_utf16
+    source = "hello"
+    assert_equal 4, RubyLsp.convert_to_byte_offset_position(source, 2, Encoding::UTF_16)
+    assert_equal 10, RubyLsp.convert_to_byte_offset_position(source, 5, Encoding::UTF_16)
+
+    # test surrogate pairs
+    source = "a😊b"
+    assert_equal 4, RubyLsp.convert_to_byte_offset_position(source, 2, Encoding::UTF_16)
+    assert_equal 6, RubyLsp.convert_to_byte_offset_position(source, 3, Encoding::UTF_16)
+  end
+
+  def test_convert_to_byte_offset_position_with_utf32
+    source = "hello"
+    assert_equal 8, RubyLsp.convert_to_byte_offset_position(source, 2, Encoding::UTF_32)
+    assert_equal 20, RubyLsp.convert_to_byte_offset_position(source, 5, Encoding::UTF_32)
+  end
+end