add some tests of set_unchecked in use

tests/set_unchecked.rs

@@ -0,0 +1,95 @@
+use salsa::Database;
+
+salsa::query_group! {
+    trait HelloWorldDatabase: salsa::Database {
+        fn input(key: ()) -> String {
+            type Input;
+            storage input;
+        }
+
+        fn length(key: ()) -> usize {
+            type Length;
+        }
+
+        fn double_length(key: ()) -> usize {
+            type DoubleLength;
+        }
+    }
+}
+
+fn length(db: &impl HelloWorldDatabase, (): ()) -> usize {
+    let l = db.input(()).len();
+    assert!(l > 0); // not meant to be invoked with no input
+    l
+}
+
+fn double_length(db: &impl HelloWorldDatabase, (): ()) -> usize {
+    db.length(()) * 2
+}
+
+#[derive(Default)]
+struct DatabaseStruct {
+    runtime: salsa::runtime::Runtime<DatabaseStruct>,
+}
+
+impl salsa::Database for DatabaseStruct {
+    fn salsa_runtime(&self) -> &salsa::runtime::Runtime<DatabaseStruct> {
+        &self.runtime
+    }
+}
+
+salsa::database_storage! {
+    struct DatabaseStorage for DatabaseStruct {
+        impl HelloWorldDatabase {
+            fn input() for Input;
+            fn length() for Length;
+            fn double_length() for DoubleLength;
+        }
+    }
+}
+
+#[test]
+fn normal() {
+    let db = DatabaseStruct::default();
+    db.query(Input).set((), format!("Hello, world"));
+    assert_eq!(db.double_length(()), 24);
+    db.query(Input).set((), format!("Hello, world!"));
+    assert_eq!(db.double_length(()), 26);
+}
+
+#[test]
+#[should_panic]
+fn use_without_set() {
+    let db = DatabaseStruct::default();
+    db.double_length(());
+}
+
+#[test]
+fn using_set_unchecked_on_input() {
+    let db = DatabaseStruct::default();
+    db.query(Input).set_unchecked((), format!("Hello, world"));
+    assert_eq!(db.double_length(()), 24);
+}
+
+#[test]
+fn using_set_unchecked_on_input_after() {
+    let db = DatabaseStruct::default();
+    db.query(Input).set((), format!("Hello, world"));
+    assert_eq!(db.double_length(()), 24);
+
+    // If we use `set_unchecked`, we don't notice that `double_length`
+    // is out of date. Oh well, don't do that.
+    db.query(Input).set_unchecked((), format!("Hello, world!"));
+    assert_eq!(db.double_length(()), 24);
+}
+
+#[test]
+fn using_set_unchecked() {
+    let db = DatabaseStruct::default();
+
+    // Use `set_unchecked` to intentionally set the wrong value,
+    // demonstrating that the code never runs.
+    db.query(Length).set_unchecked((), 24);
+
+    assert_eq!(db.double_length(()), 48);
+}