Do not create unnecessary failing assembler.

source/simulator/newton.cc

@@ -53,8 +53,10 @@ namespace aspect
 
     if (this->get_material_model().is_compressible())
       {
-        assemblers.stokes_preconditioner.push_back(
-          std::make_unique<aspect::Assemblers::StokesCompressiblePreconditioner<dim>>());
+        // The compressible part of the preconditioner is only necessary if we use the simplified A block
+        if (this->get_parameters().use_full_A_block_preconditioner == false)
+          assemblers.stokes_preconditioner.push_back(
+            std::make_unique<aspect::Assemblers::StokesCompressiblePreconditioner<dim>>());
 
         assemblers.stokes_system.push_back(
           std::make_unique<aspect::Assemblers::NewtonStokesCompressibleStrainRateViscosityTerm<dim>>());

tests/tosi_benchmark_newton_solver_full_A.cc

@@ -0,0 +1 @@
+#include <../benchmarks/tosi_et_al_2015_gcubed/tosi.cc>

tests/tosi_benchmark_newton_solver_full_A.prm

@@ -0,0 +1,15 @@
+# This is a test for the Tosi benchmark using the Newton solver and the full A block
+# as preconditioner. Prior to this test there was a bug assigning the correct assemblers
+# for this case.
+
+include $ASPECT_SOURCE_DIR/benchmarks/newton_solver_benchmark_set/tosi_et_al_2015/input.prm
+
+set Additional shared libraries            = ./libnewton_solver_tosi.so
+set End time                               = 0.0021
+set Max nonlinear iterations               = 15
+
+subsection Solver parameters
+  subsection Stokes solver parameters
+    set Use full A block as preconditioner = true
+  end
+end