Detect single unique text column in label_column_for_table, closes #2458

Also added new tests for label_column_for_table()

tests/test_label_column_for_table.py

@@ -0,0 +1,97 @@
+import pytest
+from datasette.database import Database
+from datasette.app import Datasette
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize(
+    "create_sql,table_name,config,expected_label_column",
+    [
+        # Explicit label_column
+        (
+            "create table t1 (id integer primary key, name text, title text);",
+            "t1",
+            {"t1": {"label_column": "title"}},
+            "title",
+        ),
+        # Single unique text column
+        (
+            "create table t2 (id integer primary key, name2 text unique, title text);",
+            "t2",
+            {},
+            "name2",
+        ),
+        (
+            "create table t3 (id integer primary key, title2 text unique, name text);",
+            "t3",
+            {},
+            "title2",
+        ),
+        # Two unique text columns means it cannot decide on one
+        (
+            "create table t3x (id integer primary key, name2 text unique, title2 text unique);",
+            "t3x",
+            {},
+            None,
+        ),
+        # Name or title column
+        (
+            "create table t4 (id integer primary key, name text);",
+            "t4",
+            {},
+            "name",
+        ),
+        (
+            "create table t5 (id integer primary key, title text);",
+            "t5",
+            {},
+            "title",
+        ),
+        # But not if there are multiple non-unique text that are not called title
+        (
+            "create table t5x (id integer primary key, other1 text, other2 text);",
+            "t5x",
+            {},
+            None,
+        ),
+        (
+            "create table t6 (id integer primary key, Name text);",
+            "t6",
+            {},
+            "Name",
+        ),
+        (
+            "create table t7 (id integer primary key, Title text);",
+            "t7",
+            {},
+            "Title",
+        ),
+        # Two columns, one of which is id
+        (
+            "create table t8 (id integer primary key, content text);",
+            "t8",
+            {},
+            "content",
+        ),
+        (
+            "create table t9 (pk integer primary key, content text);",
+            "t9",
+            {},
+            "content",
+        ),
+    ],
+)
+async def test_label_column_for_table(
+    create_sql, table_name, config, expected_label_column
+):
+    """Test cases for label_column_for_table method"""
+    ds = Datasette()
+    db = ds.add_database(Database(ds, memory_name="test_label_column_for_table"))
+    await db.execute_write_script(create_sql)
+    if config:
+        ds.config = {"databases": {"test_label_column_for_table": {"tables": config}}}
+    actual_label_column = await db.label_column_for_table(table_name)
+    if expected_label_column is None:
+        assert actual_label_column is None
+    else:
+        assert actual_label_column == expected_label_column