Clean up version solver tests a bit.

sdk/lib/_internal/pub/lib/src/package.dart

Index: sdk/lib/_internal/pub/lib/src/package.dart
diff --git a/sdk/lib/_internal/pub/lib/src/package.dart b/sdk/lib/_internal/pub/lib/src/package.dart
index 5e97516dfd6a79a3a9554cce7fb4d4b5fe56d6d5..e6aa20cd3e82b1e4cc1788f536d27bb0afbcb185 100644
--- a/sdk/lib/_internal/pub/lib/src/package.dart
+++ b/sdk/lib/_internal/pub/lib/src/package.dart
@@ -111,6 +111,10 @@ class _PackageName {
   /// Returns a [PackageId] for this package with the given concrete version.
   PackageId atVersion(Version version) =>
     new PackageId(name, source, version, description);
+
+  /// Returns a [PackageDep] for this package with the given version constraint.
+  PackageDep withConstraint(VersionConstraint constraint) =>
+    new PackageDep(name, source, constraint, description);
 }
 
 /// A reference to a [Package], but not any particular version(s) of it.