Autocomplete widget and /-/debug/autocomplete test page

tests/test_debug_autocomplete.py

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+import pytest
+from bs4 import BeautifulSoup as Soup
+
+from datasette.app import Datasette
+from datasette.database import Database
+
+
+@pytest.mark.asyncio
+async def test_debug_autocomplete_for_table():
+    ds = Datasette(memory=True)
+    db = ds.add_database(
+        Database(ds, memory_name="test_debug_autocomplete_for_table"), name="data"
+    )
+    await db.execute_write_script("""
+        create table authors (
+            id integer primary key,
+            name text
+        );
+        insert into authors (id, name) values
+            (1, 'Ada Lovelace'),
+            (2, 'Grace Hopper');
+    """)
+
+    response = await ds.client.get("/-/debug/autocomplete?database=data&table=authors")
+
+    assert response.status_code == 200
+    soup = Soup(response.text, "html.parser")
+    assert soup.select_one("h1").text == "Debug autocomplete"
+    assert any(
+        "autocomplete.js" in (script.get("src") or "")
+        for script in soup.find_all("script")
+    )
+    autocomplete = soup.select_one("datasette-autocomplete")
+    assert autocomplete is not None
+    assert autocomplete["src"] == "/data/authors/-/autocomplete"
+    assert soup.select_one("input#debug-autocomplete-input") is not None
+    assert "Label column:" in response.text
+    assert "<code>name</code>" in response.text
+
+
+@pytest.mark.asyncio
+async def test_debug_autocomplete_suggests_label_column_tables():
+    ds = Datasette(memory=True)
+    db = ds.add_database(
+        Database(ds, memory_name="test_debug_autocomplete_suggests"), name="data"
+    )
+    await db.execute_write_script("""
+        create table authors (
+            id integer primary key,
+            name text
+        );
+        create table releases (
+            id integer primary key,
+            title text
+        );
+    """)
+
+    response = await ds.client.get("/-/debug/autocomplete")
+
+    assert response.status_code == 200
+    soup = Soup(response.text, "html.parser")
+    links = {a.text: a["href"] for a in soup.select("table.rows-and-columns a")}
+    assert links == {
+        "authors": "/-/debug/autocomplete?database=data&table=authors",
+        "releases": "/-/debug/autocomplete?database=data&table=releases",
+    }
+    assert [code.text for code in soup.select("table.rows-and-columns code")] == [
+        "name",
+        "title",
+    ]
+
+
+@pytest.mark.asyncio
+async def test_debug_autocomplete_scan_limit():
+    ds = Datasette(memory=True)
+    db = ds.add_database(
+        Database(ds, memory_name="test_debug_autocomplete_scan_limit"), name="data"
+    )
+    await db.execute_write_script(
+        "\n".join(
+            f"create table t{i:03d} (id integer primary key);" for i in range(100)
+        )
+        + "\ncreate table z_has_label (id integer primary key, name text);"
+    )
+
+    response = await ds.client.get("/-/debug/autocomplete")
+
+    assert response.status_code == 200
+    assert "No tables with detected label columns found." in response.text
+    assert "Scanned 100 tables; stopped at the 100 table scan limit." in response.text
+    assert "z_has_label" not in response.text