Refactor version_solver_test.

lib/src/solver/backtracking_solver.dart

Index: lib/src/solver/backtracking_solver.dart
diff --git a/lib/src/solver/backtracking_solver.dart b/lib/src/solver/backtracking_solver.dart
index 7f3cc432fe51ca74cdfcccc14cfb47c0335aa02c..45fccba0cd03ef91b93221e14e3fe160dd3d32ad 100644
--- a/lib/src/solver/backtracking_solver.dart
+++ b/lib/src/solver/backtracking_solver.dart
@@ -189,6 +189,7 @@ class BacktrackingSolver {
       // 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);
     }