added tests

interpreter/tests/lox/this/closure.lox

@@ -0,0 +1,13 @@
+class Foo {
+  getClosure() {
+    fun closure() {
+      return this.toString();
+    }
+    return closure;
+  }
+
+  toString() { return "Foo"; }
+}
+
+var closure = Foo().getClosure();
+print closure(); // expect: Foo

interpreter/tests/lox/this/nested_class.lox

@@ -0,0 +1,20 @@
+class Outer {
+  method() {
+    print this; // expect: Outer instance
+
+    fun f() {
+      print this; // expect: Outer instance
+
+      class Inner {
+        method() {
+          print this; // expect: Inner instance
+        }
+      }
+
+      Inner().method();
+    }
+    f();
+  }
+}
+
+Outer().method();

interpreter/tests/lox/this/nested_closure.lox

@@ -0,0 +1,19 @@
+class Foo {
+  getClosure() {
+    fun f() {
+      fun g() {
+        fun h() {
+          return this.toString();
+        }
+        return h;
+      }
+      return g;
+    }
+    return f;
+  }
+
+  toString() { return "Foo"; }
+}
+
+var closure = Foo().getClosure();
+print closure()()(); // expect: Foo

interpreter/tests/lox/this/this_at_top_level.lox

@@ -0,0 +1 @@
+this; // Error at 'this': Can't use 'this' outside of a class.

interpreter/tests/lox/this/this_in_method.lox

@@ -0,0 +1,6 @@
+class Foo {
+  bar() { return this; }
+  baz() { return "baz"; }
+}
+
+print Foo().bar().baz(); // expect: baz

interpreter/tests/lox/this/this_in_top_level_function.lox

@@ -0,0 +1,3 @@
+fun foo() {
+  this; // Error at 'this': Can't use 'this' outside of a class.
+}