Add test cases.

frontends/benchmarks/imperative/valid/MutableTuple.scala

@@ -5,8 +5,34 @@ object MutableTuple {
   case class Foo(var value: BigInt)
   case class Bar(var value: BigInt)
 
-  def t1(pair: (Foo, Bar)) = {
+  def t1(pair: (Foo, Bar)): BigInt = {
     pair._1.value = 1
     assert(pair._1.value == 1)
+    pair._2.value
+  }
+
+  def t2() = {
+    val pair =  (Foo(1), Foo(2), Foo(3))
+    val secondFoo = pair._2
+    secondFoo.value = 4
+    assert(pair == (Foo(1), Foo(4), Foo(3)))
+    assert(pair._2.value == secondFoo.value)
+
+    pair._2.value = 6
+    assert(pair == (Foo(1), Foo(6), Foo(3)))
+    assert(pair._2.value == secondFoo.value)
+  }
+
+  def t3(): (Foo, Bar) = {
+    val bar = Bar(1)
+    val foo = Foo(2)
+    (foo, bar)
+  }
+
+  def t4() = {
+    val pair = t3()
+    pair._2.value = 100
+
+    assert(t1((pair._1, pair._2)) == 100)
   }
 }