message: Add test for preconditioner
diff: @@ -293,4 +293,32 @@ TEST_F(Gmres, SolvesBigDenseSystem1WithRestart)
  }
  +TEST_F(Gmres, SolvesWithPreconditioner)
  +{
  + auto gmres_factory_preconditioner =
  + gko::solver::Gmres<>::Factory::create()
  + .with_criterion(
  + gko::stop::Combined::Factory::create()
  + .with_criteria(
  + gko::stop::Iteration::Factory::create()
  + .with_max_iters(100u)
  + .on_executor(exec),
  + gko::stop::ResidualNormReduction<>::Factory::create()
  + .with_reduction_factor(1e-15)
  + .on_executor(exec))
  + .on_executor(exec))
  + .with_preconditioner(
  + gko::solver::Gmres<>::Factory::create().on_executor(exec))
  + .on_executor(exec);
  + auto solver = gmres_factory_preconditioner->generate(mtx_big);
  + auto b = gko::initialize<Mtx>(
  + {72748.36, 297469.88, 347229.24, 36290.66, 82958.82, -80192.15}, exec);
  + auto x = gko::initialize<Mtx>({0.0, 0.0, 0.0, 0.0, 0.0, 0.0}, exec);
  +
  + solver->apply(b.get(), x.get());
  +
  + ASSERT_MTX_NEAR(x, l({52.7, 85.4, 134.2, -250.0, -16.8, 35.3}), 1e-10);
  +}
  +
  +
  } // namespace
  