add some tests about setting with same value

tests/incremental/constants.rs

@@ -43,6 +43,15 @@ fn invalidate_constant_1() {
     db.query(ConstantsInput).set_constant('a', 66);
 }
 
+/// Test that use can still `set` an input that is constant, so long
+/// as you don't change the value.
+#[test]
+fn set_after_constant_same_value() {
+    let db = &TestContextImpl::default();
+    db.query(ConstantsInput).set_constant('a', 44);
+    db.query(ConstantsInput).set('a', 44);
+}
+
 #[test]
 fn not_constant() {
     let db = &TestContextImpl::default();

tests/incremental/memoized_inputs.rs

@@ -60,3 +60,20 @@ fn revalidate() {
     assert_eq!(v, 66);
     db.assert_log(&[]);
 }
+
+/// Test that invoking `set` on an input with the same value does not
+/// trigger a new revision.
+#[test]
+fn set_after_no_change() {
+    let db = &TestContextImpl::default();
+
+    db.query(Input1).set((), 44);
+    let v = db.max(());
+    assert_eq!(v, 44);
+    db.assert_log(&["Max invoked"]);
+
+    db.query(Input1).set((), 44);
+    let v = db.max(());
+    assert_eq!(v, 44);
+    db.assert_log(&[]);
+}