test: re-add tests for deprecated .case

ibis/backends/tests/test_generic.py

@@ -2010,6 +2010,21 @@ def test_switch_cases_null(con):
     assert con.execute(e) == "expected"
 
 
+def test_case(con):
+    # just to make sure that the deprecated .case() method still works
+    with pytest.warns(FutureWarning, match=".cases"):
+        assert con.execute(ibis.case().when(True, "yes").end()) == "yes"
+        assert pd.isna(con.execute(ibis.case().when(False, "yes").end()))
+        assert con.execute(ibis.case().when(False, "yes").else_("no").end()) == "no"
+
+        assert con.execute(ibis.literal("a").case().when("a", "yes").end()) == "yes"
+        assert pd.isna(con.execute(ibis.literal("a").case().when("b", "yes").end()))
+        assert (
+            con.execute(ibis.literal("a").case().when("b", "yes").else_("no").end())
+            == "no"
+        )
+
+
 @pytest.mark.notimpl(
     ["dask", "pandas", "polars"], raises=NotImplementedError, reason="not a SQL backend"
 )