Add tests for utils.friendly_join

tests/test_utils.py

@@ -0,0 +1,20 @@
+import pytest
+
+from tsplib95 import utils
+
+
+@pytest.mark.parametrize('items,kw,result,exc', [
+    ([], {}, '', None),
+    (list('abc'), {}, 'a, b, and c', None),
+    (list('abc'), {'limit': 3}, 'a, b, and c', None),
+    (list('a'), {'limit': 3}, 'a', None),
+    (list('ab'), {'limit': 3}, 'a and b', None),
+    (list('abcd'), {'limit': 3}, 'a, b, c, and 1 more', None),
+    (list('abcde'), {'limit': 3}, 'a, b, c, and 2 more', None),
+])
+def test_friendly_join(items, kw, result, exc):
+    if exc is not None:
+        with pytest.raises(exc):
+            utils.friendly_join(items, **kw)
+    else:
+        assert utils.friendly_join(items, **kw) == result

tsplib95/utils.py

@@ -117,10 +117,14 @@ def friendly_join(items, limit=None):
     if limit is not None:
         truncated = len(items) - limit
         items = items[:limit]
-        items.append(f'{truncated} more')
+        if truncated > 0:
+            items.append(f'{truncated} more')
 
-    *items, last = items
+    *items, last_item = items
     if not items:
-        return str(last)
+        return str(last_item)
 
-    return f'{", ".join(items)} and {last}'
+    # oxford commas are important
+    if len(items) == 1:
+        return f'{items[0]} and {last_item}'
+    return f'{", ".join(items)}, and {last_item}'