[Tests] increase coverage

Author: ljharb

implementation.js

@@ -77,19 +77,17 @@ define(MapShimPrototype, {
 			entry = SLOT.get(this, '[[storage]]')[fkey];
 			if (entry) {
 				return entry.value;
-			} else {
-				return void undefined;
 			}
+			return void undefined;
 		}
 		var map = SLOT.get(this, '[[map]]');
 		if (map) {
 			// fast object key path
 			entry = origMapGet(map, key);
 			if (entry) {
 				return entry.value;
-			} else {
-				return void undefined;
 			}
+			return void undefined;
 		}
 		var head = SLOT.get(this, '[[head]]');
 		var i = head;

test/tests.js

@@ -55,6 +55,12 @@ module.exports = function (Map, t) {
 		st.end();
 	});
 
+	t.test('throws when `.call`ed with an existing instance', function (t) {
+		var map = new Map();
+		t['throws'](function () { Map.call(map); });
+		t.end();
+	});
+
 	t.test('should accept an iterable as argument', function (st) {
 		var map = new Map();
 		testMapping(st, map, 'a', 'b', 'add "a"->"b" to map');