Ability to add descending order indexes (#262)

* DescIndex(column) for descending index columns, refs #260
* Ability to add desc indexes using CLI, closes #260

tests/test_cli.py

@@ -208,6 +208,17 @@ def test_create_index(db_path):
     )
 
 
+def test_create_index_desc(db_path):
+    db = Database(db_path)
+    assert [] == db["Gosh"].indexes
+    result = CliRunner().invoke(cli.cli, ["create-index", db_path, "Gosh", "--", "-c1"])
+    assert result.exit_code == 0
+    assert (
+        db.execute("select sql from sqlite_master where type='index'").fetchone()[0]
+        == "CREATE INDEX [idx_Gosh_c1]\n    ON [Gosh] ([c1] desc)"
+    )
+
+
 @pytest.mark.parametrize(
     "col_name,col_type,expected_schema",
     (

tests/test_create.py

@@ -1,6 +1,7 @@
 from sqlite_utils.db import (
     Index,
     Database,
+    DescIndex,
     ForeignKey,
     AlterError,
     NoObviousTable,
@@ -739,6 +740,19 @@ def test_create_index_if_not_exists(fresh_db):
     dogs.create_index(["name"], if_not_exists=True)
 
 
+def test_create_index_desc(fresh_db):
+    dogs = fresh_db["dogs"]
+    dogs.insert({"name": "Cleo", "twitter": "cleopaws", "age": 3, "is good dog": True})
+    assert [] == dogs.indexes
+    dogs.create_index([DescIndex("age"), "name"])
+    sql = fresh_db.execute(
+        "select sql from sqlite_master where name='idx_dogs_age_name'"
+    ).fetchone()[0]
+    assert sql == (
+        "CREATE INDEX [idx_dogs_age_name]\n" "    ON [dogs] ([age] desc, [name])"
+    )
+
+
 @pytest.mark.parametrize(
     "data_structure",
     (