Add tests for WaitGroup

Test 1 shows that without WaitGroup, no waiting for goroutine. Test 2 shows that WaitGroup successfully forces a join.

src/tests/test.ts

@@ -837,6 +837,57 @@ v.X // 3
     defaultNumWords
 );
 
+// Test WaitGroups
+
+testProgram(`
+
+type Vertex struct {
+    X int
+}
+
+func (v *Vertex) Add(w Vertex) {
+    v.X = v.X + w.X;
+}
+
+v := Vertex{1};
+w := Vertex{2};
+
+go func() {
+    for i := 0; i < 1000; i++ { // iterate for 1000 times to prove that waitgroup works as intended
+    }
+    v.Add(w);
+}()
+
+v.X; //1
+`, 1, '', defaultNumWords);
+
+testProgram(`
+
+type Vertex struct {
+    X int
+}
+
+func (v *Vertex) Add(w Vertex) {
+    v.X = v.X + w.X;
+}
+
+v := Vertex{1};
+w := Vertex{2};
+
+wg := WaitGroup{1};
+
+go func() {
+    for i := 0; i < 1000; i++ { // iterate for 1000 times to prove that waitgroup works as intended
+    }
+    v.Add(w);
+    wg.Done();
+}()
+
+wg.Wait();
+
+v.X; //3
+`, 3, '', defaultNumWords);
+
 // Testing struct methods with goroutines (goroutines cannot return anything)
 testProgram(
     `