feat(di): add metadata to Key

modules/di/test/di/key_spec.js

@@ -1,8 +1,12 @@
-import {describe, it, expect} from 'test_lib/test_lib';
+import {describe, it, expect, beforeEach} from 'test_lib/test_lib';
 import {Key} from 'di/di';
 
 export function main() {
   describe("key", function () {
+    beforeEach(function () {
+      Key.clear();
+    });
+
     it('should be equal to another key if type is the same', function () {
       expect(Key.get('car')).toBe(Key.get('car'));
     });
@@ -14,5 +18,32 @@ export function main() {
     it('should return the passed in key', function () {
       expect(Key.get(Key.get('car'))).toBe(Key.get('car'));
     });
+
+    describe("metadata", function () {
+      it("should assign metadata to a key", function () {
+        var key = Key.get('car');
+
+        Key.setMetadata(key, "meta");
+
+        expect(key.metadata).toEqual("meta");
+      });
+
+      it("should allow assigning the same metadata twice", function () {
+        var key = Key.get('car');
+
+        Key.setMetadata(key, "meta");
+        Key.setMetadata(key, "meta");
+
+        expect(key.metadata).toEqual("meta");
+      });
+
+      it("should throw when assigning different metadata", function () {
+        var key = Key.get('car');
+
+        Key.setMetadata(key, "meta1");
+
+        expect(() => Key.setMetadata(key, "meta2")).toThrowError();
+      });
+    });
   });
 }