Conservative transfers: added a test

that uses MultiAppCopyTransfer. But the code should work for other field transferes

Refs idaholab#12948

test/tests/transfers/multiapp_conservative_transfer/master.i

@@ -0,0 +1,75 @@
+[Mesh]
+  type = GeneratedMesh
+  dim = 2
+  nx = 10
+  ny = 10
+[]
+
+[Variables]
+  [./u]
+  [../]
+[]
+
+[Kernels]
+  [./diff]
+    type = Diffusion
+    variable = u
+  [../]
+[]
+
+[BCs]
+  [./left]
+    type = DirichletBC
+    variable = u
+    boundary = left
+    value = 0
+  [../]
+  [./right]
+    type = DirichletBC
+    variable = u
+    boundary = right
+    value = 1
+  [../]
+[]
+
+[Executioner]
+  type = Steady
+  solve_type = 'PJFNK'
+  petsc_options_iname = '-pc_type -pc_hypre_type'
+  petsc_options_value = 'hypre boomeramg'
+[]
+
+[MultiApps]
+  [./sub]
+    type = FullSolveMultiApp
+    input_files = sub.i
+    execute_on = timestep_end
+  [../]
+[]
+
+[Postprocessors]
+  [./from_postprocessor]
+    type = ElementIntegralVariablePostprocessor
+    variable = u
+    execute_on = 'INITIAL nonlinear  TIMESTEP_END'
+  [../]
+[]
+
+[Transfers]
+  [./to_sub]
+    type = MultiAppCopyTransfer
+    direction = to_multiapp
+    source_variable = u
+    variable = u
+    preserve_transfer = true
+    multi_app = sub
+  [../]
+[]
+
+[Outputs]
+  exodus = true
+  [./console]
+    type = Console
+    execute_postprocessors_on = 'INITIAL nonlinear TIMESTEP_END'
+  [../]
+[]

test/tests/transfers/multiapp_conservative_transfer/sub.i

@@ -0,0 +1,57 @@
+[Mesh]
+  type = GeneratedMesh
+  dim = 2
+  nx = 10
+  ny = 10
+[]
+
+[Variables]
+  [./u]
+  [../]
+[]
+
+[Kernels]
+  [./diff]
+    type = Diffusion
+    variable = u
+  [../]
+[]
+
+[BCs]
+  [./left]
+    type = DirichletBC
+    variable = u
+    boundary = left
+    value = 0
+  [../]
+  [./right]
+    type = DirichletBC
+    variable = u
+    boundary = right
+    value = 1
+  [../]
+[]
+
+[Postprocessors]
+  [./to_postprocessor]
+    type = ElementIntegralVariablePostprocessor
+    variable = u
+    execute_on = 'INITIAL nonlinear TIMESTEP_END'
+  [../]
+[]
+
+[Problem]
+  type = FEProblem
+[]
+
+[Executioner]
+  type = Steady
+  solve_type = 'PJFNK'
+  nl_abs_tol = 1e-12
+  petsc_options_iname = '-pc_type -pc_hypre_type'
+  petsc_options_value = 'hypre boomeramg'
+[]
+
+[Outputs]
+  exodus = true
+[]

test/tests/transfers/multiapp_conservative_transfer/tests

@@ -0,0 +1,11 @@
+[Tests]
+  issues = '#12948'
+  design = '/MultiAppCopyTransfer.md'
+  [./conservative_transfer]
+    # Tests transfer between linear Lagrange nonlinear variable
+    type = Exodiff
+    input = master.i
+    exodiff = 'master_out.e master_out_sub0.e'
+    requirement = 'MOOSE shall support conservative transfers'
+  [../]
+[]