Refactor version_solver_test.

lib/src/solver/backtracking_solver.dart

 // 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.
 
 /// A back-tracking depth-first solver.
 ///
 /// Attempts to find the best solution for a root package's transitive
 /// dependency graph, where a "solution" is a set of concrete package versions.
 /// A valid solution will select concrete versions for every package reached
 /// from the root package's dependency graph, and each of those packages will
@@ skipping 171 matching lines @@
           packages, overrides, pubspecs, _getAvailableVersions(packages),
           _attemptedSolutions);
     } on SolveFailure catch (error) {
       // Wrap a failure in a result so we can attach some other data.
       return new SolveResult.failure(systemCache.sources, root, lockFile,
           overrides, error, _attemptedSolutions);
     } finally {
       // Gather some solving metrics.
       var buffer = new StringBuffer();
       buffer.writeln('${runtimeType} took ${stopwatch.elapsed} seconds.');
+      buffer.writeln('- Tried $_attemptedSolutions solutions');
       buffer.writeln(cache.describeResults());
       log.solver(buffer);
     }
   }
 
   /// Generates a map containing all of the known available versions for each
   /// package in [packages].
   ///
   /// The version list may not always be complete. If the package is the root
   /// root package, or if it's a package that we didn't unlock while solving
@@ skipping 445 matching lines @@
   void _validateSdkConstraint(Pubspec pubspec) {
     if (_overrides.containsKey(pubspec.name)) return;
     if (pubspec.environment.sdkVersion.allows(sdk.version)) return;
 
     throw new BadSdkVersionException(pubspec.name,
         'Package ${pubspec.name} requires SDK version '
         '${pubspec.environment.sdkVersion} but the current SDK is '
         '${sdk.version}.');
   }
 }