Port MapIterator tests to wasm

crates/js-sys/tests/wasm/MapIterator.rs

@@ -0,0 +1,23 @@
+use wasm_bindgen::JsValue;
+use wasm_bindgen_test::*;
+use js_sys::*;
+
+// TODO: not much you can do with `MapIterator` types yet :(
+
+#[wasm_bindgen_test]
+fn entries() {
+    let map = Map::new();
+    assert!(JsValue::from(map.entries()).is_object());
+}
+
+#[wasm_bindgen_test]
+fn keys() {
+    let map = Map::new();
+    assert!(JsValue::from(map.keys()).is_object());
+}
+
+#[wasm_bindgen_test]
+fn values() {
+    let map = Map::new();
+    assert!(JsValue::from(map.values()).is_object());
+}