Add version validation for LookupMap, also add unittest directly in LookupMap (take 2)

pkg/lookup_map/test/lookup_map_test.dart

+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:lookup_map/lookup_map.dart';
+
+import 'package:test/test.dart';
+
+class Key {
+  final int id;
+  const Key(this.id);
+}
+
+class A{}
+const B = const Key(1);
+class C{}
+
+main() {
+  test('entries constructor', () {
+    var m = const LookupMap(const [
+        A, "the-text-for-A",
+        B, "the-text-for-B",
+        1.2, "the-text-for-1.2"]);
+    expect(m[A], 'the-text-for-A');
+    expect(m[B], 'the-text-for-B');
+    expect(m[1.2], 'the-text-for-1.2');
+    expect(m[C], null);
+    expect(m[1.3], null);
+  });
+
+  test('pair constructor', () {
+    var m = const LookupMap.pair(A, "the-text-for-A");
+    expect(m[A], 'the-text-for-A');
+    expect(m[B], null);
+  });
+
+  test('nested lookup', () {
+    var m = const LookupMap(const [],
+        const [const LookupMap.pair(A, "the-text-for-A")]);
+    expect(m[A], 'the-text-for-A');
+    expect(m[B], null);
+  });
+
+  test('entry shadows nested maps', () {
+    var m = const LookupMap(const [
+      A, "the-text-for-A2",
+    ], const [
+      const LookupMap.pair(A, "the-text-for-A1"),
+    ]);
+    expect(m[A], 'the-text-for-A2');
+  });
+
+  test('nested maps shadow in order', () {
+    var m = const LookupMap(const [ ], const [
+      const LookupMap.pair(A, "the-text-for-A1"),
+      const LookupMap.pair(B, "the-text-for-B2"),
+      const LookupMap.pair(A, "the-text-for-A2"),
+      const LookupMap.pair(B, "the-text-for-B1"),
+    ]);
+    expect(m[A], 'the-text-for-A2');
+    expect(m[B], 'the-text-for-B1');
+  });
+
+  // This test would fail if dart2js has a bug, but we keep it here for our
+  // sanity.
+  test('reachable lookups are not tree-shaken', () {
+    var m = const LookupMap(const [
+      A, B,
+      B, C,
+      C, 3.4,
+    ]);
+    expect(m[m[m[A]]], 3.4);
+  });
+}