chore: checkpoint before Python removal

vendor/bitflags/src/tests/is_empty.rs

@@ -0,0 +1,31 @@
+use super::*;
+
+use crate::Flags;
+
+#[test]
+fn cases() {
+    case(true, TestFlags::empty(), TestFlags::is_empty);
+
+    case(false, TestFlags::A, TestFlags::is_empty);
+    case(false, TestFlags::ABC, TestFlags::is_empty);
+    case(
+        false,
+        TestFlags::from_bits_retain(1 << 3),
+        TestFlags::is_empty,
+    );
+
+    case(true, TestZero::empty(), TestZero::is_empty);
+
+    case(true, TestEmpty::empty(), TestEmpty::is_empty);
+}
+
+#[track_caller]
+fn case<T: Flags + std::fmt::Debug>(expected: bool, value: T, inherent: impl FnOnce(&T) -> bool) {
+    assert_eq!(expected, inherent(&value), "{:?}.is_empty()", value);
+    assert_eq!(
+        expected,
+        Flags::is_empty(&value),
+        "Flags::is_empty({:?})",
+        value
+    );
+}