1 files changed, 51 insertions, 0 deletions
diff --git a/test/prism/ruby/source_test.rb b/test/prism/ruby/source_test.rb
new file mode 100644
index 0000000000..f7cf4fe83a
--- /dev/null
+++ b/test/prism/ruby/source_test.rb
@@ -0,0 +1,51 @@
+# frozen_string_literal: true
+
+require_relative "../test_helper"
+
+module Prism
+  class SourceTest < TestCase
+    def test_byte_offset
+      source = Prism.parse(<<~SRC).source
+      abcd
+      efgh
+      ijkl
+      SRC
+
+      assert_equal 0, source.byte_offset(1, 0)
+      assert_equal 5, source.byte_offset(2, 0)
+      assert_equal 10, source.byte_offset(3, 0)
+      assert_equal 15, source.byte_offset(4, 0)
+
+      error = assert_raise(ArgumentError) { source.byte_offset(5, 0) }
+      assert_equal "line 5 is out of range", error.message
+
+      error = assert_raise(ArgumentError) { source.byte_offset(0, 0) }
+      assert_equal "line 0 is out of range", error.message
+
+      error = assert_raise(ArgumentError) { source.byte_offset(-1, 0) }
+      assert_equal "line -1 is out of range", error.message
+    end
+
+    def test_byte_offset_with_start_line
+      source = Prism.parse(<<~SRC, line: 11).source
+      abcd
+      efgh
+      ijkl
+      SRC
+
+      assert_equal 0, source.byte_offset(11, 0)
+      assert_equal 5, source.byte_offset(12, 0)
+      assert_equal 10, source.byte_offset(13, 0)
+      assert_equal 15, source.byte_offset(14, 0)
+
+      error = assert_raise(ArgumentError) { source.byte_offset(15, 0) }
+      assert_equal "line 15 is out of range", error.message
+
+      error = assert_raise(ArgumentError) { source.byte_offset(10, 0) }
+      assert_equal "line 10 is out of range", error.message
+
+      error = assert_raise(ArgumentError) { source.byte_offset(9, 0) }
+      assert_equal "line 9 is out of range", error.message
+    end
+  end
+end