Test edge case in current_line directly

A pragma: no cover was removed from StringReader.current_line and its useless edge case was given its own test.

parsita/state.py

@@ -144,7 +144,7 @@ def next_token(self) -> str:
 
     def current_line(self):
         characters_consumed = 0
-        for line_index, line in enumerate(StringIO(self.source)):  # pragma: no cover
+        for line_index, line in enumerate(StringIO(self.source)):
             if characters_consumed + len(line) > self.position:
                 # The line with the error has been found
                 character_index = self.position - characters_consumed

tests/test_state.py

@@ -43,3 +43,10 @@ def test_state_creation(self):
         error = ParseError('Expected a but found b at index 0')
         self.assertEqual(str(error), 'Expected a but found b at index 0')
         self.assertEqual(repr(error), "ParseError('Expected a but found b at index 0')")
+
+    def test_current_line(self):
+        # This test only exists to get 100% test coverage without doing a pragma: no cover on the whole current_line
+        # method. Under normal operation, the for loop should never complete because the position is also on some
+        # line. Here, the position has been artificially advanced beyond the length of the input.
+        reader = StringReader('foo', 3)
+        self.assertEqual(reader.current_line(), None)