1 files changed, 43 insertions, 0 deletions
diff --git a/compiler/rustc_data_structures/src/snapshot_map/tests.rs b/compiler/rustc_data_structures/src/snapshot_map/tests.rs
new file mode 100644
index 000000000..72ca53c2b
--- /dev/null
+++ b/compiler/rustc_data_structures/src/snapshot_map/tests.rs
@@ -0,0 +1,43 @@
+use super::SnapshotMap;
+
+#[test]
+fn basic() {
+    let mut map = SnapshotMap::default();
+    map.insert(22, "twenty-two");
+    let snapshot = map.snapshot();
+    map.insert(22, "thirty-three");
+    assert_eq!(map[&22], "thirty-three");
+    map.insert(44, "forty-four");
+    assert_eq!(map[&44], "forty-four");
+    assert_eq!(map.get(&33), None);
+    map.rollback_to(snapshot);
+    assert_eq!(map[&22], "twenty-two");
+    assert_eq!(map.get(&33), None);
+    assert_eq!(map.get(&44), None);
+}
+
+#[test]
+#[should_panic]
+fn out_of_order() {
+    let mut map = SnapshotMap::default();
+    map.insert(22, "twenty-two");
+    let snapshot1 = map.snapshot();
+    map.insert(33, "thirty-three");
+    let snapshot2 = map.snapshot();
+    map.insert(44, "forty-four");
+    map.rollback_to(snapshot1); // bogus, but accepted
+    map.rollback_to(snapshot2); // asserts
+}
+
+#[test]
+fn nested_commit_then_rollback() {
+    let mut map = SnapshotMap::default();
+    map.insert(22, "twenty-two");
+    let snapshot1 = map.snapshot();
+    let snapshot2 = map.snapshot();
+    map.insert(22, "thirty-three");
+    map.commit(snapshot2);
+    assert_eq!(map[&22], "thirty-three");
+    map.rollback_to(snapshot1);
+    assert_eq!(map[&22], "twenty-two");
+}