added tests

interpreter/tests/lox/field/get_and_set_method.lox

@@ -0,0 +1,25 @@
+// Bound methods have identity equality.
+class Foo {
+  method(a) {
+    print "method";
+    print a;
+  }
+  other(a) {
+    print "other";
+    print a;
+  }
+}
+
+var foo = Foo();
+var method = foo.method;
+
+// Setting a property shadows the instance method.
+foo.method = foo.other;
+foo.method(1);
+// expect: other
+// expect: 1
+
+// The old method handle still points to the original method.
+method(2);
+// expect: method
+// expect: 2