added tests

interpreter/tests/lox/for/scope.lox

@@ -0,0 +1,26 @@
+{
+  var i = "before";
+
+  // New variable is in inner scope.
+  for (var i = 0; i < 1; i = i + 1) {
+    print i; // expect: 0
+
+    // Loop body is in second inner scope.
+    var i = -1;
+    print i; // expect: -1
+  }
+}
+
+{
+  // New variable shadows outer variable.
+  for (var i = 0; i > 0; i = i + 1) {}
+
+  // Goes out of scope after loop.
+  var i = "after";
+  print i; // expect: after
+
+  // Can reuse an existing variable.
+  for (i = 0; i < 1; i = i + 1) {
+    print i; // expect: 0
+  }
+}