Add function and unit tests for boundary layer mixing

For the near-boundary lateral mixing, the indices of the layers that
are spanned by the boundary layer need to be returned. Additionally,
in cases where the boundary layer intersects partway through a layer,
the non-dimensional position also needs to be returned for polynomial
reconstructions to be evaluated correctly. Six unit tests were added
to test this new function.

All unit tests currently pass

src/core/MOM_unit_tests.F90

@@ -5,10 +5,11 @@ module MOM_unit_tests
 
 use MOM_error_handler,     only : MOM_error, FATAL, is_root_pe
 
-use MOM_string_functions,  only : string_functions_unit_tests
-use MOM_remapping,         only : remapping_unit_tests
-use MOM_neutral_diffusion, only : neutral_diffusion_unit_tests
-use MOM_diag_vkernels,     only : diag_vkernels_unit_tests
+use MOM_string_functions,          only : string_functions_unit_tests
+use MOM_remapping,                 only : remapping_unit_tests
+use MOM_neutral_diffusion,         only : neutral_diffusion_unit_tests
+use MOM_diag_vkernels,             only : diag_vkernels_unit_tests
+use MOM_boundary_lateral_mixing,   only : near_boundary_unit_tests 
 
 implicit none ; private
 
@@ -35,6 +36,9 @@ subroutine unit_tests(verbosity)
        "MOM_unit_tests: neutralDiffusionUnitTests FAILED")
     if (diag_vkernels_unit_tests(verbose)) call MOM_error(FATAL, &
        "MOM_unit_tests: diag_vkernels_unit_tests FAILED")
+    if (near_boundary_unit_tests(verbose)) call MOM_error(FATAL, &
+       "MOM_unit_tests: near_boundary_unit_tests FAILED")
+
   endif
 
 end subroutine unit_tests