[tests] fix deprecated `df.visualize` usages

dune/gdt/test/burgers/base.hh

@@ -92,8 +92,9 @@ public:
                      std::min(this->T_end_, this->time_points_from_vector_array(solution.dof_vectors()).back());
                  for (size_t ii = 0; ii < this->visualization_steps_; ++ii) {
                    const double time = ii * (end_time / this->visualization_steps_);
-                   solution.evaluate(time).visualize(XT::Common::Test::get_unique_test_name() + "__" + prefix
-                                                     + "_solution_" + XT::Common::to_string(ii));
+                   GDT::visualize(solution.evaluate(time),
+                                  XT::Common::Test::get_unique_test_name() + "__" + prefix + "_solution_"
+                                      + XT::Common::to_string(ii));
                  }
                })
     , visualization_steps_(0)

dune/gdt/test/linear-transport/base.hh

@@ -99,8 +99,9 @@ public:
                      std::min(this->T_end_, this->time_points_from_vector_array(solution.dof_vectors()).back());
                  for (size_t ii = 0; ii < this->visualization_steps_; ++ii) {
                    const double time = ii * (end_time / this->visualization_steps_);
-                   solution.evaluate(time).visualize(XT::Common::Test::get_unique_test_name() + "__" + prefix
-                                                     + "_solution_" + XT::Common::to_string(ii));
+                   GDT::visualize(solution.evaluate(time),
+                                  XT::Common::Test::get_unique_test_name() + "__" + prefix + "_solution_"
+                                      + XT::Common::to_string(ii));
                  }
                })
     , visualization_steps_(0)

dune/gdt/test/stokes/stokes-taylorhood.hh

@@ -314,12 +314,12 @@ public:
       bool visualize = true;
       std::string grid_name = XT::Common::Typename<G>::value();
       if (visualize) {
-        sol_u_func.visualize("solution_u_" + type + "_" + grid_name);
-        sol_p_func.visualize("solution_p_" + type + "_" + grid_name);
-        reference_solution_u.visualize("u_ref_" + grid_name);
-        actual_p_ref.visualize("p_ref_" + grid_name);
-        u_diff.visualize("u_error_" + type + "_" + grid_name);
-        p_diff.visualize("p_error_" + type + "_" + grid_name);
+        GDT::visualize(sol_u_func, "solution_u_" + type + "_" + grid_name);
+        GDT::visualize(sol_p_func, "solution_p_" + type + "_" + grid_name);
+        GDT::visualize(reference_solution_u, "u_ref_" + grid_name);
+        GDT::visualize(actual_p_ref, "p_ref_" + grid_name);
+        GDT::visualize(u_diff, "u_error_" + type + "_" + grid_name);
+        GDT::visualize(p_diff, "p_error_" + type + "_" + grid_name);
       }
       DXTC_EXPECT_FLOAT_LE(l2_norm(problem_.grid_view(), u_diff), expected_error_u);
       DXTC_EXPECT_FLOAT_LE(l2_norm(problem_.grid_view(), p_diff), expected_error_p);