Add tests for field id clashes

glowtables/table.py

@@ -61,7 +61,7 @@ class Field(abc.ABC, Generic[_TFieldValue]):
         to ``subject_var``.
 
         For example, if this ``Field`` represents the `"CPU frequency"
-        <https://www.wikidata.org/wiki/Property:P2144>`, ``subject_var`` is ``a``, and
+        <https://www.wikidata.org/wiki/Property:P2144>`__, ``subject_var`` is ``a``, and
         ``object_var`` is `b``, this will return::
 
             ?subject_var <http://www.wikidata.org/prop/direct/P2144> ?object_var.

glowtables/tests/table_test.py

@@ -14,6 +14,7 @@
 
 import textwrap
 
+import pytest
 import rdflib
 
 from glowtables.table import Language, LiteralField, Table
@@ -90,3 +91,35 @@ def test_default_value() -> None:
         }
         """
     )
+
+
+def test_field_id_subject() -> None:
+    name_field = LiteralField(
+        "subject",
+        {Language("en"): "Name"},
+        rdflib.URIRef("http://example.org/display-name"),
+    )
+    with pytest.raises(ValueError, match="both subject and a field id"):
+        Table(
+            fields=[name_field],
+            constraints="",
+        )
+
+
+def test_field_id_clash() -> None:
+    name_field = LiteralField(
+        "name",
+        {Language("en"): "Name"},
+        rdflib.URIRef("http://example.org/name"),
+    )
+    display_name_field = LiteralField(
+        "name",
+        {Language("en"): "Display Name"},
+        rdflib.URIRef("http://example.org/display-name"),
+    )
+    with pytest.raises(ValueError, match="has duplicate field ids: name"):
+        Table(
+            fields=[name_field, display_name_field],
+            constraints="",
+        )
+