correctly highlight lines with tabs

testline.py

@@ -0,0 +1,30 @@
+import unittest
+
+from line import Line
+
+
+class MyTestCase(unittest.TestCase):
+    def test_column_to_char(self):
+        byte_offset = 123
+        text = "\tabc"  # will be rendered as: ........abc  where . represents a whitespace column
+        line = Line(byte_offset=byte_offset, byte_end=byte_offset + len(text.encode("utf8")), line=text)
+
+        self.assertEqual(0, line.column_to_char(0))  # the tab
+        self.assertEqual(0, line.column_to_char(1))  # the tab
+        self.assertEqual(0, line.column_to_char(3))  # last column of the tab
+        self.assertEqual(1, line.column_to_char(4))  # a
+        self.assertEqual(2, line.column_to_char(5))  # b
+        self.assertEqual(3, line.column_to_char(6))  # c
+
+    def test_char_to_column(self):
+        byte_offset = 123
+        text = "\tabc"  # will be rendered as: ........abc  where . represents a whitespace column
+        line = Line(byte_offset=byte_offset, byte_end=byte_offset + len(text.encode("utf8")), line=text)
+        self.assertEqual(0, line.char_to_column(0))
+        self.assertEqual(4, line.char_to_column(1))
+        self.assertEqual(5, line.char_to_column(2))
+        self.assertEqual(6, line.char_to_column(3))
+
+
+if __name__ == '__main__':
+    unittest.main()