message: Add a Mass+Diffusion test.
diff: @@ -93,7 +93,12 @@ std::string getString(CeedCoeffType coeff_type)
  return "";
  }
  -enum class Problem {Mass, Convection, Diffusion, VectorMass, VectorDiffusion};
  +enum class Problem { Mass,
  + Convection,
  + Diffusion,
  + VectorMass,
  + VectorDiffusion,
  + MassDiffusion };
  std::string getString(Problem pb)
  {
  @@ -114,6 +119,9 @@ std::string getString(Problem pb)
  case Problem::VectorDiffusion:
  return "VectorDiffusion";
  break;
  + case Problem::MassDiffusion:
  + return "MassDiffusion";
  + break;
  }
  mfem_error("Unknown Problem.");
  return "";
  @@ -230,6 +238,12 @@ void test_ceed_operator(const char* input, int order, const CeedCoeffType coeff_
  k_ref.AddDomainIntegrator(new VectorDiffusionIntegrator(*coeff));
  k_test.AddDomainIntegrator(new VectorDiffusionIntegrator(*coeff));
  break;
  + case Problem::MassDiffusion:
  + k_ref.AddDomainIntegrator(new MassIntegrator(*coeff));
  + k_test.AddDomainIntegrator(new MassIntegrator(*coeff));
  + k_ref.AddDomainIntegrator(new DiffusionIntegrator(*coeff));
  + k_test.AddDomainIntegrator(new DiffusionIntegrator(*coeff));
  + break;
  }
  k_ref.Assemble();
  @@ -316,7 +330,7 @@ TEST_CASE("CEED mass & diffusion", "[CEED]")
  {
  auto assembly = GENERATE(AssemblyLevel::PARTIAL,AssemblyLevel::NONE);
  auto coeff_type = GENERATE(CeedCoeffType::Const,CeedCoeffType::Grid,CeedCoeffType::Quad);
  - auto pb = GENERATE(Problem::Mass,Problem::Diffusion,
  + auto pb = GENERATE(Problem::Mass,Problem::Diffusion,Problem::MassDiffusion,
  Problem::VectorMass,Problem::VectorDiffusion);
  auto order = GENERATE(1);
  auto mesh = GENERATE("../../data/inline-quad.mesh","../../data/inline-hex.mesh",
  