Avoid network requests while resolving versions when possible.

sdk/lib/_internal/pub/test/get/hosted/avoid_network_requests_test.dart

Index: sdk/lib/_internal/pub/test/get/hosted/avoid_network_requests_test.dart
diff --git a/sdk/lib/_internal/pub/test/get/hosted/avoid_network_requests_test.dart b/sdk/lib/_internal/pub/test/get/hosted/avoid_network_requests_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..cd66d84ae35141b8d1fb7746958d3b8abb54ff66
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+++ b/sdk/lib/_internal/pub/test/get/hosted/avoid_network_requests_test.dart
@@ -0,0 +1,63 @@
+// Copyright (c) 2012, 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.
+
+library pub_tests;
+
+import 'package:scheduled_test/scheduled_test.dart';
+
+import '../../descriptor.dart' as d;
+import '../../test_pub.dart';
+
+main() {
+  initConfig();
+
+  integration('only requests versions that are needed during solving', () {
+    servePackages([
+      packageMap("foo", "1.0.0"),
+      packageMap("foo", "1.1.0"),
+      packageMap("foo", "1.2.0"),
+      packageMap("bar", "1.0.0"),
+      packageMap("bar", "1.1.0"),
+      packageMap("bar", "1.2.0")
+    ]);
+
+    d.appDir({
+      "foo": "any"
+    }).create();
+
+    // Get once so it gets cached.
+    pubGet();
+
+    // Clear the cache. We don't care about anything that was served during
+    // the initial get.
+    getRequestedPaths();
+
+    // Add "bar" to the dependencies.
+    d.appDir({
+      "foo": "any",
+      "bar": "any"
+    }).create();
+
+    // Run the solver again.
+    pubGet();
+
+    d.packagesDir({
+      "foo": "1.2.0",
+      "bar": "1.2.0"
+    }).validate();
+
+    // The get should not have done any network requests since the lock file is
+    // up to date.
+    getRequestedPaths().then((paths) {
+      expect(paths, unorderedEquals([
+        // Bar should be requested because it's new, but not foo.
+        "api/packages/bar",
+        // Should only request the most recent version.
+        "api/packages/bar/versions/1.2.0",
+        // Need to download it.
+        "packages/bar/versions/1.2.0.tar.gz"
+      ]));
+    });
+  });
+}